Think you've had bad boyfriends? Linda Zevallos once dated "The Jinx" subject Robert Durst. Shown: Robert Durst sits in a police vehicle as he leaves New Orleans courthouse March 17, 2015. He was arrested in New Orleans Saturday on a murder warrant issued by the LAPD. Reuters

Talk about the ex from hell. Once upon a time, Dallas resident Linda Zevallos, now 64, dated the notorious subject of HBO's docuseries "The Jinx," Robert Durst. Zevallos told New York Daily News that she briefly dated the wealthy real-estate scion in 2000, but stopped seeing him after she found him snooping in her purse -- on the same day he wanted to go to Blockbuster to rent "American Psycho." The 2000 film starring Christian Bale is about an investment banking exec by day, serial killer by night.

Zevallos was prompted to think about Durst again when she heard about the "cadaver letter" Durst might have sent the LAPD alerting them of Durst friend Susan Berman's death in 2000. Rifling through old papers in 2008, she discovered that she, too, received a letter from Durst in the same green ink. The "cadaver letter" becomes the sensational clue that links Durst to Berman's murder in "The Jinx," when a letter with similarities in spelling and writing of Durst's is given to the docuseries' director. Durst was charged with Berman's murder and is currently being held without bail in New Orleans.

"I thought, 'Oh dear.' It was in green ink," she told New York Daily News. "It was so creepy. I'm still creeped out by the whole thing, 15 years later." She said that Durst called her and breathed on the phone for months until November 2000, one month before Berman's murder.

"I don't have any doubts that he killed Susan Berman and his wife," Zevallos told New York Daily News. "I think he has issues with abandonment. I think it's probably because his mother killed herself. He told me he was raised by a governess. He's psycho. Maybe he wanted to be the American Psycho," she said.

Police across the country are now looking into the possibility that Durst could be connected to a number of open missing-persons cases, including Lynne Kathryn Schulze, an 18-year-old Middlebury College student in 1971 and two California teens, Karen Mitchell and Kristen Modafferi, in 1997. Even former Texas judge Susan Criss, who presided over his trial for killing and dismembering Morris Black in Galveston (charges he was acquitted of), had suspicions. Criss told "Inside Edition" that she thinks Durst is a serial killer, and that it was Durst who left a cat's severed head on her doorstep.

“This was a perfectly clean and preserved cat head cut up by someone who knew what they were doing laying right there,” Judge Criss said. “I strongly believe it was Robert Durst.”