Why do people kill? A Manhattan real estate publicist and freelance writer has been penning letters to murderers behind bars to find out exactly what makes them tick. Kelly Kreth, 44, told Dailymail.com that after having a traumatic encounter with a sociopath in her own life she became inspired to learn about the inner workings of a criminal mind. Six years and 600 prison letters later, Kreth says she's learned that a sociopath is a person 'who wants to feel like the smartest person in the room.' Her own trauma: Kelly Kreth told Dailymail.com that after having a traumatic encounter with a sociopath in her own life she became inspired to learn about the inner workings of a criminal mind . Conceptual prison: In order to make initial contact with the prisoners, Kreth sent a postcard that had an image of her in a striped dress along with a note saying she thinks everyone lives in a type of prison . 'They do it for the thrill,' she said, adding that she does not condone any of the perpetrators crimes. Kreth has written to men and women behind bars who she believes fit the bill of a sociopath and who have a certain level of intelligence so that they are able to discuss their crimes in a conceptual manner. The New York Post reports that the list of the killers Kreth interacted with include Michael Swango, a doctor who poisoned as many as 60 patients in a variety of different hospitals for over two decades. 'I love it: the sweet, close, husky smell of indoor homicide,' Swango wrote in a notebook presented by prosecutors in 2000. Another killer she dared to write  was Sarah Joe Pender who was sentenced to life in prison for the murder of a couple that she and her boyfriend shared a house with in 2000. Hundreds of letters: Six years and 600 prison letters later, Kreth says she's learned that a sociopath is a person 'who wants to feel like the smartest person in the room' Kreth also wrote to Ira Einhorn, a hippie who helped to found Earth Day. In 1979 police found his ex-girlfriends body beaten and mummified in his closet in 1979. She even reached out to prisoner Thomas 'Bart' Whitaker, a man on death row for the murder of his devout Christian family in 2003. In order to make initial contact with the prisoners, Kreth sent a postcard that had an image of her in a striped dress. She planned to open conversation by saying that prison goes beyond padlocked walls. 'I wanted to discuss how conceptually everyone lives in their own type of prison.' Kreth says she shared personal information about her own life so that the prisoners saw her as someone they would feel comfortable sharing their secrets with. 'Sociopaths spend their whole life acting,' Kreth told Dailymail.com . 'They can tell when people are being fake or genuine. I waited two years before asking them the questions about what makes them a true sociopath.' Hippy killer: Fugitive Ira Einhorn who killed his ex-girlfriend  told Kreth that he is not a sociopath but found manipulating people easy . Kreth said one of her most interesting interactions was with the hospital killer Michael Swango. ‘Love your look; love your age, Kelly,' Swango wrote Kreth in a  2009 letter, adding, 'Would love to get to know you much better. EXPLORE ALL THINGS INSIDE and OUTSIDE . . . I hope you’re not shy.' Kreth said she made it clear to prisoners that her interactions to them were not romantic, though it was her picture that got their attention. She says she would send Swango articles in publications in the New Yorker about sociopaths and that he would then circle parts of the story he felt were true characteristics of a killer. ‘A sociopath wants to feel like he is the smartest person in the world,’ Swango told her. When asked if he had guilt or remorse, Swango wrote, ‘The short answer to your question is, ‘nothing at all That’s why it went on for so long. No deep thoughts, or confusion, or remorse or anything else.’ Lady killer: Another killer she dared to write was Sarah Joe Pender who was sentenced to life in prison for the murder of a couple that she and her boyfriend shared a house with in 2000 . When asked if sociopath’s feel he wrote, ‘I would disagree that a sociopath can “neither feel empathy or true love.” One can be “empathetic” to some people or things and not to others. Where is the line between love, obsessive love, or something that looks like any of the above, but is not…? You & I could have a long discussion on the exact meaning of this phrase! Many gradations, many shades of gray between pure while & pure darkness/evil!’ Swango, Kreth told the Post, would sign his letters very bizarrely. ‘Sometimes he would sign his notes "You know you love me, XOXO, Gossip Girl,"” Kreth said. ‘He’s a 60 year old guy, who has maybe murdered 60 people, who’s into poison, and writing, ‘hey girl’ . . . and ‘OMG we must talk about ebola.’ ‘It’s darkly funny,’ she said. When speaking to Ira Einhorn who killed his girlfriend, Einhorn said that he doesn't see himself as a sociopath but told her that 'manipulation is the easiest thing in the world.' 'I’m an empath, so calling me, labeling me as a sociopath is silly.When you’re intelligent & have some ability to introspect, you early on or eventually realize that it is easy to manipulate almost everyone you meet. You or I made a choice: No manipulation which people often take as the ultimate manipulation. Too easy! Not interesting — what is of great interest is direct open communication which is what I did for years in the 70s,' he wrote. Murdered his parents: Thomas Bart Whitaker told Kreth he admits to being a sociopath and says he murdered his parents because they 'didn't love him' Thomas Bart Whitaker never admitted to being a sociopath but said he always felt different form other people. 'You are correct about being born with the wrong wiring. Some of us just don’t have things set up upstairs like everyone else,' he wrote her in a letter. An alleged killer Kreth has been dying to interview is millionaire Robert Durst who has been linked to three murders but never convicted. Durst, who was heir to a vast real estate empire before becoming estranged from his family, was arrested last month for the suspected 2000 murder of his friend, writer Susan Berman, in Los Angeles. ‘Durst once stole a sandwich for $6 but had $37,000 with him in his car. It’s because he wanted to feel the thrill. He seems like the true definition of a sociopath.’ Writing to killers has helped Kreth to heal and has also provided fascinating insight into a criminal's mind. She told Dailymail.com she hopes to write a book.
Kelly Kreth had a traumatic encounter with a sociopath in her own life and became inspired to learn about the inner workings of a criminal mind .
Six years and 600 prison letters later, Kreth says a sociopath is a person 'who wants to feel like the smartest person in the room'
'They do it for the thrill,' Kreth said, adding that she does not condone any of the perpetrators crimes .
Kreth says she wants to write to alleged murderer Robert Durst .