Denver ? Eric Harris and Dylan Klebold showed signs of depression and violent fantasies two years before their suicidal rampage at Columbine High School, according to an upcoming TV documentary.

Bullying at school prompted sadness and resentment, and violent images in film and video games helped push Harris and Klebold into anger and depression, researchers say in the “Investigative Reports” program airing on the cable network A&E on April 15.

Klebold and Harris killed 13 people and wounded 23 before killing themselves inside the school in 1999.

One classmate, who is not identified in the documentary, said Harris told his psychology class of a recurring dream in which he awakes, comes to school and starts shooting students and teachers and then blows up the school.

Students also said the gunmen made a video for a classroom assignment called “Hitmen for Hire.”

Nate Dykeman, a classmate who was a friend of both teens, said Harris’ parents found a pipe bomb when they searched their son’s room.

“They were furious about it and then kept it in their room because they didn’t know what to do with it,” he said.

In their lawsuits, victims’ families have alleged that deputies were aware that Harris’ father, Wayne Harris, found a pipe bomb made by his son and exploded it in a vacant field.

Wayne Harris has denied that he found such a bomb.

The show follows psychiatrists and a former FBI agent on the Newport, Calif.-based Threat Assessment Group, which sought to develop “psychiatric autopsies” of Harris and Klebold. The team’s conclusions will not be released until the documentary airs.