Angel of Death: Killer nurse stopped, but not soon enough

The following is a script from "Angel of Death" which aired on April 28, 2013. Steve Kroft is the correspondent. Graham Messick, producer.

Tonight you're going to come face-to-face with a serial killer, one of the most prolific serial killers in U.S. history. They don't usually talk to reporters. And in the 45 years of 60 Minutes, we have never interviewed one until now.

Charles Cullen was a critical care nurse who admits to killing up to 40 people. Some suspect it was a lot more. The murders took place over 16 years in seven different hospitals. There were suspicions at nearly all of them that Cullen was harming patients, yet none of them passed that information on to subsequent employers. Newspaper headlines called him "The Angel of Death," but as you will see, Charles Cullen was no mercy killer. Until we interviewed him a few weeks ago, he had never spoken publically about his crimes, never tried to explain why he did it, or even express remorse to the families of victims when he finally faced them in court.

Thomas Strenko: This monster didn't even know us or our son, but had the audacity to end his life.

Richard Stoeker: I'd like to tell you a little about my mother, that you murdered. You don't even have the guts to look this way do you?

Clara Hardgrove: Charles. Why don't you look up at us?! I'd like to show you what you did to our children. This is their dad in his coffin. How do you like that?

This was the scene seven years ago at the Somerset County Courthouse in New Jersey, as Charles Cullen sat through his sentencing hearing, refusing to speak, or even acknowledge the family members of people he had murdered. Even the judge was exasperated.

Judge Paul Armstrong: Mr. Cullen, I asked you a question...Why is it that you have chosen not to address the court?...Can you hear me, Mr. Cullen?"

He's kept that silence behind the walls of the New Jersey State Prison in Trenton, where he is in protective custody to keep him safe from other inmates. Protecting himself from his own demons has been more difficult. We found out when we sat down across from him in a cramped cubicle separated by a thick layer of glass, to talk about the people he's killed.

Steve Kroft: Is 40 an arbitrary number?

Charles Cullen: Forty is an estimate. I gave a number between 30 and 40. I think I have identified, you know, most of them.

Steve Kroft: Look, you pled guilty to murder. But you don't use that word.

Charles Cullen: I think that I had a lot of trouble accepting that word for a long time. I accept that that's what it is.

Steve Kroft: Do you consider yourself a serial killer?

Charles Cullen: I mean, I guess it depends upon a person's definition. If it's more than one and it's a pattern, I guess then yes.

In Cullen's case, all his victims were patients assigned to hospital units where he worked as a nurse. They ranged in age from 21 to 91. Some were critically ill. Others were ready to be discharged when Cullen injected them with drugs that would kill them. It was a pattern that began 26 years ago at St. Barnabas Medical Center in Livingston, New Jersey, Cullen's very first nursing job.

Charles Cullen: I worked on the burn unit. So, I mean, there was a lot of pain, a lot of suffering. And I didn't cope with that as well as I thought I would.

Steve Kroft: And that was the first place that you gave someone medication that caused them to die?

Charles Cullen: Yes.

The patient was John Yengo, a judge from New Jersey, who was suffering from a severe case of sunburn, until Cullen injected him with a fatal overdose of lidocaine.

Steve Kroft: Do you remember the person?

Charles Cullen: I mean, I remember one and that's the only person I've been able to identify.

But there could have been more...St. Barnabas didn't know about the patient Cullen murdered, but it did suspect him of trying to kill or harm a half dozen other patients by randomly and repeatedly poisoning bags of saline solution.

Charles Graebar: Someone was spiking IV bags with insulin in the store room.

Charles Graeber, a New York writer as well as a former medical student and researcher, has spent seven years investigating Cullen's murders for a new book called "The Good Nurse." Graeber says a number of patients at St. Barnabas went into insulin shock and nearly died.

Charles Graeber: He was the main suspect for poisoning random bags of saline. If you talked to the investigators there, they'll tell you, "Cullen was our man. We knew he was dirty." They couldn't prove anything. It's all circumstantial.

Steve Kroft: They fire him?

Charles Graeber: He moved on.

When Cullen left the hospital, the insulin overdoses stopped.

Charles Cullen: At St. Barnabas, they could've had my license investigated and probably revoked at that point in time.

Steve Kroft: Should they have?

Charles Cullen: Should they have? Yes.

But instead of ending Charles Cullen's nursing career, St. Barnabas marked the beginning of a 16-year killing spree.

Cullen would work at eight other hospitals and be suspected of harming patients at six of them, but those suspicions never reached subsequent employers and Cullen continued to murder patients with virtual impunity. In 1993, prosecutors investigated Cullen for murdering 91-year-old Helen Dean. An autopsy tested for nearly 100 medications, but not the one Cullen used to kill her: a powerful drug called digoxin, or dig for short. It was Cullen's first weapon of choice.

Steve Kroft: Why did you like dig?

Charles Cullen: Dig, you know, it was a very powerful cardiac medication.

Steve Kroft: What does it do to someone?

Charles Cullen: In small amounts, it slows the heart rate down. In larger amounts, it can cause what's called complete heart block. And then, the heart is very irregular. And you know, it can cause death. It does cause death, in large amounts.

It was also readily available in critical care units, and Cullen figured out ways to conceal his digoxin withdrawals from an automatic drug dispensary system called Pyxis, which required nurses to type in the name of the patient and the drug to be administered.

Charles Cullen: I wouldn't go in for dig. I would go under Tylenol or another medication that would be in the same drawer. /So, you know, there was no record of me going in for dig other than the fact that, you know, it was in the same drawer.

Steve Kroft: How did you choose who you're going to give this medication to?

Charles Cullen: It's difficult for me to go back in time and think about what things were running through my mind at the time.

Steve Kroft: Was it personal?

Charles Cullen: No, no.

Steve Kroft: Did you get pleasure out of it? Satisfaction? Relief?

Charles Cullen: No, I thought that people weren't suffering anymore. So, in a sense, I thought I was helping.

Cullen suggested several times that his actions were merciful, but the evidence doesn't support it. 60-year-old Elenor Stoecker, an asthma patient, was recovering and in no pain when Cullen administered a fatal digoxin overdose. College student Michael Strenko, who suffered from an autoimmune disease, was recovering from what his parents called routine surgery to remove his spleen.

Mary Strenko (at sentencing): My heart it aches for my son. It bleeds for my son.

Thomas Strenko (at sentencing): We vividly remember, Charles Cullen walking into the waiting room. He looked us right in the eye and stated how Michael was gravely ill and people don't make it. And my wife told Cullen, "That's enough. You can leave now." We're haunted by the memory of Charles Cullen coming to the waiting room to get our reaction.

Steve Kroft: There were people that you caused to die, who were not near death, and not suffering that much

Charles Cullen: You know, again, you know, I mean, my goal here isn't to justify. You know what I did there is no justification. Um, I just think that the only thing I can say is that I felt overwhelmed at the time.

Steve Kroft: Can you give us anything? Can you give the families anything? Any explanation for how this happened and why this happened?

Charles Cullen: Like I said, I --I can't -- I just can't say that. It was more or less, you know, it felt like I needed to do something. And, I, I did. And that's not an answer to anything.

Charles Cullen was the youngest of eight children and grew up poor on this street in West Orange, New Jersey, protected by his mother. Cullen was 17 when she died. He tried to kill himself. He spent six years in the Navy, most of them as a missile technician on a nuclear submarine. He was miserable, felt bullied, tried to kill himself again. After receiving a general discharge, he decided to take up nursing. He got married and started a family, but it all went sour. A messy divorce, custody battles, bankruptcy, heavy drinking, more half-hearted suicide attempts and trips to the psychiatric ward... that was Charles Cullen's state of mind when he was killing people, and on the night he finally confessed to the murders.

Charles Cullen (confession): I tried to kill myself throughout my life because I never really liked being who I was. 'Cause I didn't think I was worthy of anything.

Charles Graeber: It was never about anyone but Charlie Cullen. He did what he did because of his own needs, his own compulsions.

Author Charles Graeber interviewed Cullen more than a dozen times for his book. And he remembers seeing words like paranoid, major depression, hostile, passive-aggressive and anti-social on psychiatric reports.

Charles Graeber: He sees himself as a victim. And as a victim, he's entitled to lash out in any way he wants to make things right. If that means killing patients, anything justifies his victimhood.

Steve Kroft: You said at one point that you thought it was about power and control. What do you mean?

Charles Graeber: If the rest of his life was spinning out of control, if he was losing custody, if he was feeling depressed, if his love life was in the toilet, he could poison patients, he could save patients. He could make decisions. He had an arena in which he mattered, and where his actions had definite consequences.

Steve Kroft: Here you have a person who tried to kill himself at least 20 times, who is in and out of psych wards. And on some occasions, walked right out of the psych ward and right into a job as a critical care nurse.

Charles Graeber: Right, he actually took a call asking him back on shift from a psych ward.

Steve Kroft: Why wouldn't the hospitals do some background checks?

Charles Graeber: Well partially because they weren't required to and partially because there was a nursing shortage on. Charlie Cullen looked good. By the end of his career, he was a 16-year veteran. He had recommendations. And for a hospital to ask too much or say too much became a liability. You can't penalize a nurse for seeking counseling, for seeking treatment, for going to a rehab center successfully. And so because of that, Charlie hid in those shadows.

When Cullen was hired at Saint Luke's University Hospital in Bethlehem, Penn., he had been fired or forced to resign from five other hospitals. Yet none of this was in his file with the state nursing board. By his own count, Cullen had already murdered 11 people. And he would kill at least five more at Saint Luke's. Nurses were suspicious, there were rumors about his past, and Cullen was caught red-handed stealing lethal drugs. But instead of calling the police Saint Luke's brought in a lawyer to confront Cullen.

Steve Kroft: Do you think that they knew what you were doing at St. Luke's?

Charles Cullen: I think that they had a strong suspicion.

Steve Kroft: Did you expect to get caught?

Charles Cullen: Well, I think you can say I was caught at St. Barnabas, and I was caught at St. Luke's. There's no reason that I should've been a practicing nurse after that.

Steve Kroft: They offered you some kind of a deal?

Charles Cullen: They said, "If you resign, we'll give you neutral references." And I decided to go with that.

Steve Kroft: What is it about this system and about hospitals that no one went to police, no one really wanted to find out what was going on. They gave you an opportunity to leave.

Charles Cullen: I think because it's a matter of worrying about lawsuits. If they pointed out that there was a problem they were going to be found liable for millions of dollars. They just saw it as a lot easier to not put themselves in a position of getting sued.

After Charles Cullen was escorted out the door of Saint Luke's Hospital with no consequences, one of the nurses called a friend at the Pennsylvania state police with her suspicions, and an investigation was begun. By then, Cullen had already found another job at the Somerset Medical Center in New Jersey. He would murder another 13 people there, but it would be his final stop. That story, when we come back.

In September 2002, when Charles Cullen was hired as a critical care nurse at New Jersey's Somerset Medical Center, the hospital knew nothing about his dark past. It didn't know that he had been fired or forced to resign at a half a dozen hospitals -- or that he'd been investigated by authorities for harming patients. And there was no reason to suspect that Cullen had murdered five patients at his last job. He was able to move from hospital to hospital without so much as a bad reference. Cullen would kill another 13 people at Somerset in 13 months and try and kill three more before two detectives, a state bureaucrat and a female nurse finally connected the dots.

Steve Kroft: You were under suspicion at St. Luke's. Yet you went off to Somerset and kept doing exactly the same things and it looks like, to me, that you wanted to get caught.

Charles Cullen: I don't know.

Steve Kroft: You don't know?

Charles Cullen: Because, you know, you're right. I mean, I continued. But I was also-- I was also careful. I was also-- deny it any time anybody would ask me.

It was the suspicious death of a Roman Catholic priest named Florian Gall that set in motion the events that would eventually expose Charles Cullen. Reverend Gall had died unexpectedly overnight while recovering from pneumonia, and the hospital discovered high levels of the heart drug digoxin in his blood. It was the second unexplained overdose in two weeks.

Steven Marcus: The blood levels were astronomical. They were way higher than you would ever shoot for by using the drug therapeutically.

Dr. Steven Marcus is the director of New Jersey's Poison Control Center. He heard about the digoxin overdoses when a pharmacist at Somerset called his office asking for help with some dosage calculations. The pharmacist also confided that two more patients in the same unit had turned up with abnormally high levels of insulin.

Steve Kroft: What's going through your mind?

Steven Marcus: My number one, two, and three thought was that there was something malicious going on in the institution.

In July of 2003, Marcus set up an urgent conference call with the hospital's medical director, Dr. William Cors, and taped the conversation in which he told the hospital to notify the authorities.

Steven Marcus: This is a police matter.

William Cors: What we're wrestling with is, you know, throwing the whole institution into chaos, versus, you know, responsibility to, you know, protect patients from further harm. And we have been trying to investigate this to get some more information before we made any kind of rush to, you know, judgment.

Steven Marcus: If there is somebody out there that is purposely doing this to individuals at your hospital, we have a legal obligation to report this.

William Cors: OK.

Somerset Medical Center would eventually notify authorities, but it would take them three long months.

Steve Kroft: Do you know how many patients died between those-

Steven Marcus: No, I don't know the number, but I do know that there were some patients that died in between that, yes -

Steve Kroft: Five.

Steven Marcus: That we know of, that you're saying.

Steve Kroft: But those -

Steven Marcus: Those five deaths will - I'll - I'll remember them the rest of my life. Sorry.

Steve Kroft: They didn't have to happen.

Steven Marcus: Right. They, they should have been preventable, yes.

It was October, before Somerset county detectives Tim Braun and Daniel Baldwin finally met with hospital officials. They were told about a half dozen incidents in the critical care unit. No one used the word "homicide."

Tim Braun: They had dropped a couple names on us with regards to their own internal investigation that they claim to have conducted for several months. And they did provide us two names in particular but did not identify them as any type of suspect or anything like that.

Steve Kroft: One of them was Charles Cullen?

Daniel Baldwin: Yes. Right.

The detectives ran a routine background check on Charles Cullen and discovered that he had been arrested for stalking a female nurse and breaking into her apartment in Easton, Penn. The file there also contained a Post-it note saying that the Pennsylvania State Police had called just a few weeks earlier asking similar questions. Detective Baldwin called the trooper who made the inquiry and hit paydirt.

Daniel Baldwin: After speaking with the trooper he informed me that his agency had conducted an investigation on Mr. Cullen with the suspicion that he was murdering patients in Pennsylvania as well. That he was using digoxin to murder patients.

Steve Kroft: And you found this out making two phone calls?

Daniel Baldwin: Yes, basically.

Tim Braun: That - that was it.

Steve Kroft: Did you think you had your man?

Daniel Baldwin and Tim Braun: Yes.

But the detectives knew that proving it would be difficult. A number of law enforcement agencies had tried and failed.

Steve Kroft: How helpful was the hospital in this investigation?

Tim Braun: How helpful was the hospital? They were very helpful by answering court-issued subpoenas. That was the extent of their cooperation.

When the detectives asked to see computerized records from the automated drug dispensary in the critical care unit, they say the hospital told them that wasn't possible because drug dispensing machines only stored records for 30 days. They learned otherwise from the machine's manufacturer.

Steve Kroft: They lied to you?

Tim Braun: Yes, they did.

Steve Kroft: They didn't want to give you records that turned out to be crucial to your investigation.

Tim Braun: Yes, that's, that's correct.

Steve Kroft: You think they tried to obstruct your investigation?

Tim Braun: They didn't try to help it. That's for sure.

When the detectives informed Somerset that Charles Cullen was the target of their investigation, the hospital fired him not for harming patients - for lying on his job application.

Steve Kroft: Did you get the sense at Somerset, for example, that any of your colleagues, any of nurses, any of the doctors knew what was going on?

Charles Cullen: No. I mean, until, you know, of the day I was fired, I mean, nobody gave me any indication that anybody was suspicious. I mean, the weird thing about Somerset Hospital was is that they were planning on firing me the night before. So they let me work one more shift knowing that they were going to fire me the next day. So they let me work an additional shift with the suspicion that I had harmed patients. Which I, you know, was kind of a bizarre thing to do.

Steve Kroft: Did you harm anybody that night?

Charles Cullen: No.

With Cullen gone and the medical center uncooperative, Detectives Braun and Baldwin decided they needed an ally inside the hospital to help them gather evidence to make their case. They decided to approach Amy Ridgway, a critical care nurse who worked with Cullen on the night shift and was his best friend at the hospital.

Amy Ridgway: He was always early, always on time, crisp. And sat down and was very serious about getting to work.

Steve Kroft: Did you consider him to be a good nurse?

Amy Ridgway: I did.

When the detectives first interviewed Ridgway, she was hostile and upset that Cullen had been fired. So they decided to show her the evidence they had gathered: the Pyxis records showing Cullen's drug withdrawals from the dispensary, and his real employment history.

Steve Kroft: What did you tell her, do you remember?

Daniel Baldwin: I just told her that he was released from several facilities. There were allegations about him at other facilities for doing similar things that that were going on at Somerset Medical Center. I guess, at that point, she realized it couldn't be a coincidence.

Steve Kroft: And she offered to help?

Daniel Baldwin: Yes.

Amy Ridgway: Danny pushed this piece of paper across the table to me. And it was the Pyxis printouts. And I was devastated. I knew. I knew he was murdering people.

Steve Kroft: How did you know that?

Amy Ridgway: There were so many withdrawals of lethal medications. There's no reason. No reason except, if you wanna kill someone.

Steve Kroft: Were you angry?

Amy Ridgway: I was sad for my patients. I was..um..so many things were going through my mind. I was sad I didn't see it. I felt betrayed by my own intuition.

Amy Ridgway, who later persuaded Cullen to do the interview with us, spent days analyzing medical records, and schooled them on a computerized record system that would help reconstruct Cullen's activities on specific days. She recorded phone conversations with Cullen and wore a wire at a meeting in this restaurant, the same day a newspaper article reported that he was being investigated for killing patients.

Amy Ridgway: I said, "I know you're guilty. I know you did this. And yet I'm still here. I'll take you down to the station. We'll go together." And he changed. His face just changed.

Steve Kroft: And what did he say?

Amy Ridgway: He said, "I want to go down fighting. I want to go down fighting.

Cullen told us he suspected that the police were listening in.

Charles Cullen: I knew that Amy had helped the police. I strongly suspected that she was wired when she was asking me those questions, so, you know, that didn't stop me having the same opinion of Amy, which is that she's a good nurse, that she's a caring nurse, and that she did it because she felt it was the right thing to do.

He was arrested right after that meeting on what the police admit was mostly circumstantial evidence. What they needed was a confession. But Cullen refused to say anything. So once again the police turned to Amy Ridgway for help.

Steve Kroft: What did you say to get him to confess?

Amy Ridgway: I wasn't very honest with him. And there's a part of me I still feel guilty about that. I was, I was manipulating him a bit. I told him, I told him the investigators were also looking at me and how could he think that I wasn't somehow going to be implicated. I remember saying to him, "So who was your first victim? And was it a long time ago? Was it recent?" And he started to talk. He said it was a long time ago.

Charles Cullen confession tape: "...it was with a medication to drop the blood pressure."

Cullen's formal confession with the detectives would last seven hours.

Charles Graeber: We will never know how many people Charlie Cullen killed.

Charles Graeber spent seven years investigating the case for his book "The Good Nurse."

Charles Graeber: It's very difficult going back, there is no paperwork, no bodies to exhume. He's working over 16 years. In Saint Barnabas alone, he later told investigators he was dosing three to four people a week. He didn't always know their outcomes.

Steve Kroft: How many do you think?

Charles Graeber: I would be very surprised, as would pretty much everyone I've spoken to with any knowledge of this case, if it was not in the 100's, multiple 100's.

Steve Kroft: You've been in here a while.

Charles Cullen: Nine years.

Steve Kroft: You knew it was wrong?

Charles Cullen: Yes, I did.

Steve Kroft: At the time?

Charles Cullen: At the time. And later.

Steve Kroft: Are you sorry, what you did?

Charles Cullen: Yes. But like I said, I don't know if I would've stopped.