Was a college student targeted because she resembled her killer's ex?

Jackie Vandagriff was found brutally murdered in a park. Was the college student targeted because she resembled the killer's ex-girlfriend? CBS News chief investigative and senior national correspondent Jim Axelrod reports in "The Murder of Jackie Vandagriff." 

On a September night in 2016, a young man strolls into a college bar in Denton, Texas, and takes a seat. He chats easily with the women around him and seems like any other carefree student out for the night.

But Charles Bryant is not who he seems. The 29-year-old doesn't attend the University of North Texas, located just across the street. In fact, he's barred from even stepping foot on campus because his ex-girlfriend, freshman Caitlin Mathis, has a restraining order against him. Just six days prior, he was arrested for stalking her and his night on the town is actually carefully planned to be within the conditions of his bond. As Bryant flirts with women at Fry Street Public House, no one knows his behavior is about to take a deadly turn.

Catlin Mathis was 18 years old when she met Bryant, a personal trainer and bartender, in June 2016.

"He was definitely smooth," Mathis told "48 Hours." "It seemed like he kind of had his life together."

With an easy-going attitude and a chiseled appearance, Bryant made a great first impression on Mathis, who was working as a server at Buffalo Wild Wings in Grapevine, Texas, and had just graduated from high school. Bryant was 11 years older than Mathis.

"He was very charming," Mathis recalled.

But Bryant's friendly façade would fade after only weeks of dating.

"He was very controlling. He always had to know where I was," Mathis said.

During an interview with correspondent Jim Axelrod, Mathis said she started to recognize that Bryant was a bit of a narcissist.

"He needed my constant attention," Mathis said.

As she started the fall semester at the University of North Texas in Denton, Mathis decided to break up with Bryant. He didn't take the news well, and things escalated quickly. When Bryant appeared at her dorm room the day after their breakup, Mathis called university police who banned him from campus. Undeterred, Bryant repeatedly contacted her. But Mathis was not interested in reconciling.

"At that point, I was scared," Mathis recalled.

And she had a good reason to be. On September 6 – what would have been their 3-month anniversary – Bryant once again found his way to Mathis' dorm room. Carrying a bouquet of flowers and a two-page letter, he slipped by the security desk and knocked on Mathis' door. Terrified, she hid in a closet and called 911. Bryant fled and was promptly arrested by campus police for a second time.

Mathis wouldn't see Bryant again as a free man, though he didn't stray far from UNT. Four days after bonding out of jail on a stalking charge for continuing to harass his ex, Bryant was just a half a mile away from Mathis' dorm room at Fry Street Public House.  

Earlier in the day, he'd spoken to his attorney about the case against him and knew he was facing more time behind bars. As Bryant sipped drinks and chatted up college girls, they had no idea what was going on in his head. But there is at least one man who says he does.

"I think he enters the bar in mission mode," said Texas Ranger James Holland. "I think he was going to kill someone that night no matter what."

A sought-after expert in high-profile murder cases across the country, Ranger Holland specializes in psychopathic and sociopathic crimes for the Texas State Police.

Tragically, a young woman named Jacqueline Vandagriff also walked into the bar on a mission that September night. The 24-year-old was looking for a job.

Vandagriff was studying nutrition at Texas Woman's University in Denton and had no known connection to Bryant. Their introduction plays out on video surveillance, as Jackie talks to the bartender about a possible position.

Just hours after meeting Bryant, Vandagriff was dead. Her mutilated body was discovered at Grapevine Lake on Sept. 14, 2016. But how she died, and why, were questions no one could answer — until Ranger Holland got the suspected killer talking.

Bryant was already in custody with the Grapevine Police Department for violating the restraining order by emailing his ex-girlfriend in the days following the murder.

After Grapevine police hit a wall in their interrogation, Holland was brought in for his expertise. Bryant, who showed no remorse and was eerily calm as police questioned him, fit the bill for extreme anti-social behavior. Holland has developed his own brand of interview techniques for cold-blooded killers who normally confound investigators.

"I think of it almost like mind-bending. You're dealing with someone who's controlling, manipulative and is trying to almost impress their will upon you," Holland said. "They feel that, at the end of the day, they can change your mind. And what you're basically doing is stepping in the back door of their mind and steering them without them knowing it."

After interviewing Bryant for six hours, Holland theorized that Bryant couldn't handle his ex-girlfriend's rejection, and that he took revenge on the next woman he could find. That woman happened to be Jackie Vandagriff.

"I think at the end of the day, she's in the wrong place at the wrong time. And she looked too much like his ex-girlfriend," Holland said.

Mathis agrees with Holland's theory, and feels lucky to be alive.

"I don't know if he wanted to send a message to me or just to express his anger," she said. "He just took things way, way out of hand."

In his 26-year career in law enforcement, Holland has investigated hundreds of murders. Vandagriff's case stood out to him on multiple levels. Not only was it a particularly gruesome crime scene, with the body dismembered and burned, but it was also unsophisticated. The Ranger said it had all the hallmarks of a serial killer's first victim. 

"Often times, if you can find the initial murder that a serial killer committed, you'll find a disheveled crime scene. They make mistakes. It's their first time," Holland said.

Vandagriff's purse was found at Bryant's house, and there was evidence that he attempted to bury her body in his backyard before moving it to Grapevine Lake and setting it on fire.  

"I think that this was his disheveled murder. Was he going to stop? Why would he?" Holland said. "There's no doubt in my mind that if Bryant had not been arrested by the Grapevine Police Department, he would have continued to kill. And he would have gotten better. And I think as he got better and better, it would have been almost impossible to catch him."

Prosecutor Anna Hernandez thinks Holland is right and believes Bryant might have been in the midst of more murderous plans when he was arrested for Vandagriff's case.

"She might have just been victim number one with Caitlin being victim number two," Hernandez said.

While she never imagined Bryant was capable of murder, Mathis still struggles with the guilt that she couldn't warn Vandagriff – a woman she didn't know – about Bryant's troubling behavior before it was too late. And her heart breaks for the Vandagriff family, whose grief is immense.

"I just wish I could take that pain away from them. I look back at it now, and I'm extremely thankful to be here. There's a reason I'm here," Mathis said.

It's why she's sharing her story today.

"As long as I can maybe help one other person out there, that means a lot to me," Mathis said.

Learn how police zeroed in on Charles Bryant in "The Murder of Jackie Vandagriff,"  airing Saturday, August 14 at 10/9c on CBS.