Long before the mayhem and murder associated with Robert Durst, a Westchester woman says she saw a side of him that scared her to death. 

The former girlfriend of Robert Durst says she saw troubling warning signs - long before Durst was convicted of killing his best friend, admitted to dismembering his neighbor and faced charges for the murder of his first wife. She says it has haunted her for years.

Penny Goldsmith is sharing her story publicly for the first time with News 12 senior investigative reporter Tara Rosenblum. 

The billionaire developer's son was smitten with the 20-year-old student from Rye back when they were college sweethearts in the 1960s. 

"He was unlike anybody I've ever met," she says. 

Both were from Westchester, but the couple first crossed paths on a mission trip to Israel. 

Goldsmith was a student at Wheelock College in Boston. Durst was a graduate student at UCLA.  The couple dated long distance for a year and a half, including a memorable 10-day visit to California during which she says Durst couldn't wait to introduce Goldsmith to his best friend, Susan Berman. 

Soon after the introduction on the West Coast, the couple traveled to the East Coast and introduced one another to their families. 

"My mother perceived him to be an unhappy human being, and it really concerned her," she says. 

A few months later, Goldsmith says Durst did something that confirmed those concerns. 

"I got a letter from him, and it started out he was driving, and he stopped a hitchhiker. and there was a gun in the car. The hitchhiker picked the gun up and pointed it at Bob and said, 'I'm going to kill you,' and Bob said 'So kill me. I'll be dead. What's dead? I don't care.' And it went on and on, and I found it really frightening. You know, it was that life had no meaning," she says. 

She remembers showing the letter to her psychology professor at the time, the noted author A. Nicholas Groth, who told her exactly how to respond. 

"He said, 'You can't see him again, he is a sociopath,'" she says. 

Goldsmith says she broke up with Durst the next day. 

Later that year, she claims she received a phone call out of the blue that still haunts her today. 

"He called me one night at 10 o'clock and said, 'I want you to come up to South Salem now.' And he said, 'Take a train to Grand Central. I'll pick you up at the Katonah train station,'" she says. "I've always wondered what would have happened to me had I gone that night. I'm sure I would not be sitting here. I think had I gone up to South Salem that night, he would have killed me."

A few years later, Durst went on to marry Kathie McCormack, who vanished after he says he dropped her off at the same train station he asked Goldsmith to meet him at. 

Durst is now facing a murder charge in Westchester four decades later. 

Durst could not be reached for comment on this story.