University of Louisville professor Ron Holmes has never met a serial killer he didnt like. Except John Wayne Gacey. For Holmes, who has helped law enforcement agencies worldwide pry into the minds of killers in 527 murder cases, that says a lot. Holmes teaches classes on sex crimes, homicides and psychological profiling and has met and interviewed many infamous people associated with sexual homicides. He has seen Charles Manson across a prison visitation room and described Ted Bundy as a charming guy. A crime scene is a painting of the bad guy, Holmes said Wednesday during a talk at Western Kentucky University. Hes telling you everything you need to know. A trained profiler can learn information about the killers age, neatness and personality just from evidence left at the scene, he said. Holmes, a former CIA agent and parole officer, became interested in profiling serial killers in sexual homicides in 1983, after a woman he knew in Louisville was found dead at a grizzly crime scene. The elderly woman had been stabbed more than 200 times and decapitated. Her killer turned out to be Cleo Green of Louisville, who believed he was being chased and attacked by floating demons, Holmes said. Had I known what I know now about profiling, it would have been easy to profile Mr. Green, Holmes said. Green, who lived near the woman, was found to be mentally ill; he was caught and convicted after trying to kill another woman, Holmes said. As Holmes delved into his research on killers, he had trouble sleeping and, for years, slept on his bedroom floor against the door, he said. Many serial killers cannot control the impulses that take control of their actions, he said. By the time they are caught, they have been killing for 20 years often starting with animals but get caught because they stop paying attention to details, Holmes said. Such killers have experienced a major break during their childhood and have bizarre fetishes and a fascination with certain body parts, he said. Between 100 and 150 serial killers exist around the world, though many of them will never be caught, Holmes said. There are some people who are bad boys and they grow up to be bad men, Holmes said. I think we need to try to understand them, but I dont think they should ever see the light of day.