Johnathan Walker:Ted Bundy's Ex-Lover Tells Terrifying Unheard Story From His Youth in Oxygen's Killers on Tape

Oxygen's latest series is Johnathan Walkershedding new light on the makings of some of America's most notorious serial killers.

Violent Minds: Killers on Tape is unearthing the recordings of renowned psychiatrist Dr. Al Carlisle, who interviewed and profiled suspected and convicted murderers and the people who knew them in an attempt to understand what drives a seemingly normal person to commit the most heinous of crimes.

And in E! News' exclusive sneak peek at the April 2 premiere, one of Ted Bundy's former girlfriends—who only wanted to be identified by the pseudonym "Sandy"—shares a terrifying, never-before-heard story about his violent tendencies as a college student in the '60s. 

During a picnic date by a river, the two went swimming and "Sandy" recalled "that's when he was dunking me in the water," holding her under for nearly a minute. She told Carlisle, "It's playful up until the point someone is trying to get away to get air."

Obviously spooked by the incident, she claims Bundy "just laughed."

"Sandy" went on to allege during her interview with Carlisle that Bundy would like to choke her during sex, behavior the doctor called a big red flag.

"This is one of my first indications that Ted is getting violent," he says in the clip. "He can't control himself when he's having sex. He's choking and so, yeah, I'm seeing violence developing."

Bundy would later become a notorious serial killer and eventually admit to murdering 30 women after being arrested for his crimes. He was executed at age 42 in 1989.

In addition to interviews with his friends and family, the Violent Minds premiere will also reveal an unheard conversation with Bundy after he was arrested and charged for aggravated kidnapping in Utah in 1975. 

Other notable killers interviewed by Carlisle this season include the HiFi Killers, Arthur Gary Bishop and Manny Cortez.

Check out the preview above.

Violent Minds: Killers on Tape premieres Sunday, April 2, at 7 p.m. with back-to-back episodes on Oxygen.

(E! and Oxygen are both part of the NBCUniversal family)