Friends and family of victims along with the whole nation try to make sense of why 64-year-old Stephen Paddocks pulled the trigger in the country's worst mass shooting. FOX News Radio spoke with forensic psychiatrist Dr. Michael Welner about how someone can commit such a crime.

Listen to the interview below:

Dr Michael Welner is a forensic psychiatrist and Chairman of The Forensic Panel. He has worked on numerous mass homicide cases and leads landmark research that invites public participation in refining standards of evil in crime, at www.depravitystandard.org.