Could the Boston Marathon bombings have been prevented?

BOSTON - It was a shocking slaying in a Boston suburb that sometimes goes years without one homicide, let alone three at once. The victims' throats had been sliced in a home on a tree-lined street, marijuana and cash strewn over their bodies.

The investigation languished for more than 18 months until just a few days after the Boston Marathon explosions, when the FBI identified the suspected bombers as Tamerlan Tsarnaev, 26, and his brother, Dzhokhar Tsarnaev, 19, ethnic Chechens who emigrated from Russia to the U.S. about a decade ago.

"Let's put it this way: If they had arrested Tamerlan as one of the killers in the triple killing before the marathon bombing, it certainly would have affected the outcome of the marathon bombing," said Waltham City Councilor Gary Marchese. "He would have been in jail and would have been tried for murder."

The brothers lived in Cambridge, across the Charles River from Boston. In March 2011, months before the September killings to the west in Waltham, Russian authorities had told the FBI they worried that Tamerlan Tsarnaev and his mother, who lives in Russia, were religious extremists. The Russians were unresponsive when pressed for more details. The FBI didn't find any derogatory information on Tsarnaev, and a criminal case was not opened. The FBI shared its results with Russia in summer 2011, shortly before the Waltham killings.

The U.S. government has wrestled with what more it could have done to prevent the marathon bombings, which killed three people and injured more than 260 others a year ago Tuesday. The FBI believes the Tsarnaev brothers acted alone and had no ties to foreign terrorist organizations.

The FBI's former executive assistant director, Stephanie Douglas, told "60 Minutes" that when she learned that Tamerlan Tsarnaev had been interviewed by the FBI two years before the bombings she was concerned.

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"We went back there and we had every piece of paper we could possibly have on Tamerlan within probably the first half hour after we identified him," she said. "What do we know about him? Because we knew that that would be a question and obviously we wanted to know what we had on him."

The assessment done by the agent was very thorough, she said.

"He not only interviewed Tamerlan, but he interviewed his parents, he went to his school, he actually drove by his house a couple of times to identify vehicles with him," she said. "He did a very thorough job and I read those interviews - nothing to suggest anything other than just the information that was in the file, nothing to suggest a threat, a national security threat."

The agent had left his card with the brothers' parents and asked that Tamerlan Tsarnaev call him.

"And Tamerlan did call," Douglas said. "He did call to set up that interview. So it wasn't like we had to go hunt him down. And I think he actually even volunteered to provide assistance if the FBI ever wanted assistance in the future."

It took 100 hours for Boston's terrorism task force to crack the bombing case.

It turned out the critical evidence had been collected before the first bomb went off.

Douglas and Rick DesLauriers, who was special agent in charge of Boston, described the wealth of surveillance video that painted a picture of the crime. Was there a eureka moment in terms of the video?

"You can see an individual, a tall man wearing a white ball cap, walk into the frame," Douglas said. "He has a backpack slung over one of his shoulders. Je puts the backpack down very nonchalantly. He joins the crowd. You clearly see everybody look very, very definitely to the left like they've heard something, they've seen something. So you know that first blast has gone off. He does not do that. He does not do what everybody else in that video does, he does not turn to his left. He instead just stands there for a second or two and walks very deliberately back the same direction that he came in."

The "eureka video" hasn't been seen by the public. It is being kept for the trial.

Only two days had passed and they were looking for every image of the suspect they called "White Hat." Massachusetts state police analysts found him with a man in a black hat.

They turned out to be Dzhokhar Tsarnaev and Tamerlan Tsarnaev.

That it took more than 18 months for law enforcement to get a lead on the 2011 slayings has angered the victims' friends and relatives. They're asking the same pressing question the federal review didn't address: What might have happened on April 15, 2013, if one of the bombing suspects had been arrested months earlier for the Waltham deaths?

"If investigators didn't write it off as just another three drug dealers dead and assumed that these deaths were not as important, then maybe the Boston Marathon bombing might not have happened," said Krysta Voskowsky, one of Mess' friends.

Law enforcement isn't talking. County prosecutor Marian Ryan and Waltham Police Chief Keith MacPherson, who inherited the case after taking office, have called the investigation active and will not answer questions about whether Tamerlan Tsarnaev is a suspect. Waltham detectives referred questions to Ryan's office. Gerry Leone, the county prosecutor at the time of the killings, has declined to comment.

"It's been an amazing black hole of information," said Marchese, the city councilor. "There's nothing."

No one has indicated that Tamerlan's brother, heading for trial in the bombings, is also a suspect.

The U.S. has long been worried about a domestic attack carried out by ideologues not tied to a larger terrorist group. A mantra emerged after the Sept. 11 attacks - "Homeland security is hometown security" - meaning local police are the first lines of defense in rooting out terrorists.

In Waltham, property crime is the most routinely reported offense, according to FBI reports. Murders are so rare that a police map detailing reported crimes doesn't even list homicide as a search category. So when Mess, Erik Weissman and Raphael Teken were found nearly decapitated on Sept. 12, 2011, it came as a shock.

The killings stunned residents of the dead-end street where Mess lived. Hours after the bodies were found, a prosecutor told reporters that there was no sign of a break-in and that the victims probably knew their killers.

Little else was heard about the investigation until after the marathon, but details are few on how police made the connection.

Tamerlan Tsarnaev, Todashev and Mess trained at the same Boston gym. Todashev was shot dead in May by an FBI agent during an interrogation at his home near Orlando. Authorities recently cleared the agent, saying Todashev had charged at a Massachusetts trooper.

Federal authorities have said that Todashev implicated Tamerlan in the Waltham slayings. But at the request of Massachusetts prosecutors, the Justice Department did not release details of the confession.

It's unclear which leads investigators might have pursued immediately after the Waltham deaths.

Jamal Abu Rubieh, owner of Brookline Lunch, the restaurant in Cambridge that Mess frequented, said he was surprised he never heard from police. Weissman and Tamerlan Tsarnaev ate there with Mess a few times.

It's routine for investigators of a killing to talk to anyone who had regular contact with the victim.

"Nobody ever came to talk to us," Rubieh said.

Even though officials insist the state is running the investigation - standard procedure except in Massachusetts' largest cities - federal authorities also appear interested. In January, a federal grand jury subpoenaed Tsarnaev's wife, Katherine Russell, asking her for things that belonged to Mess, including a leather jacket, said Amato DeLuca, her lawyer.

County and federal prosecutors declined to comment on the subpoena. It's not clear why the federal grand jury would want Mess' belongings, and Russell's lawyer said she does not have anything that belongs to Mess.