The boy accused of shooting dead two classmates in the US talked of going on a shooting spree, it is claimed.
Charles Andrew Williams allegedly opened fire at Santana High School, San Diego, killing two pupils and injuring 13.
Pupils said the 15-year-old, who has been arrested, was taunted relentlessly at school for being scrawny.
Chris Reynolds, 29, whose son was friends with Williams, said the boy stayed at his house on Saturday night and talked about going on a shooting spree.
"I even mentioned Columbine to him. I said I don't want a Columbine here. But he said, 'No, nothing will happen, I'm just joking'," Mr Reynolds said.
"I should've stepped up, even if it wasn't true and stuff, to take that precaution. That's going to be haunting me for a long time. It just hurts, because I could've maybe done something about it."
The attack was the deadliest US school shooting since Columbine in the April 1999.
Students Bryan Zuckor, 14, and Randy Gordon, 17, were killed. Zuckor was killed in the bathroom. Gordon died at a hospital.
Eleven other students, a 29-year-old student teacher and a 22-year-old campus security guard were wounded. Another student suffered minor injuries when he crashed his car fleeing the campus.
Student Jessica Moore said: "He was picked on because he was one of the scrawniest guys. People called him freak, dork, nerd, stuff like that."
Williams will be charged as an adult with murder, assault with a deadly weapon and gun possession, said San Diego County District Attorney Paul Pfingst. He was to be arraigned on Wednesday. President George W. Bush called the shooting "a disgraceful act of cowardice."