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 .