Rex Heuermann is accused of leading a deadly double life while appearing as a family man inside his Massapequa Park home.

News 12's Kevin Vesey spoke with a criminal justice expert for a glimpse into the mind of the alleged Gilgo Beach serial killer.

David Sarni, of John Jay College of Criminal Justice, believes that Heuermann thought he would never get caught.

"You could tell he enjoyed it - going over, detail-oriented...," Sarni says. "He saw he made mistakes and wrote it down to rectify those mistakes later on..."