How the Pelosi Attack Suspect Plunged Into Online Hatred

“You would talk about politics, and he was just not rational,” Mr. Ciccarelli said. “He just thought that one side was lying, and one side was telling the truth. It was very black and white. And it was just being reinforced.”

Mr. Ciccarelli, who took Mr. DePape to Thanksgiving and Christmas meals and was the closest thing to family that Mr. DePape had in recent years, suggested in an interview that Mr. DePape was tormented by his emotions.

“So he disassociated, and he dealt with his feelings by basically playing computer games whenever he wasn’t working,” Mr. Ciccarelli said. “He had no friends. He had no social life.”

Back in British Columbia, Mr. DePape’s relatives and former acquaintances tried to reconcile the news of the brutal attack on Mr. Pelosi with the person they once knew well.

Gene DePape, Mr. DePape’s stepfather, who for a time “raised him as my own” after he divorced Mr. DePape’s mother, described his stepson as good-natured and quiet, and as someone who never got into trouble. But he said he grew concerned about his stepson when, as a teenager, David appeared to grow increasingly isolated and became obsessed with video games.

Gene DePape said he tried for years to reconnect with his stepson, to no avail.

Mark DePape, David DePape’s uncle, said he had not seen his nephew in more than 20 years.

“He just decided one day: He was gone,” Mark DePape said.

One high school acquaintance, Loretta Court Brisco, described David DePape in a Facebook message as someone “not seeking to be noticed or stand out.” Another, Alisha Mills, said he was “impressionable” and “a bit of a follower.”