Michael Adebowale, one of the suspects in the Woolwich murder of Drummer Lee Rigby, saw a friend “literally sliced to pieces” when they were both teenagers.
Lee James, a bare-knuckle fighter who was suffering from a drug-induced psychotic episode, murdered 18-year-old Faridon Alizada in 2008 and also stabbed Adebowale, then 16.
The Old Bailey heard that the youths were members of the "Woolwich Boys" gang.
The judge said that the dead man had been literally cut to pieces in an early morning attack at a flat in Erith, southeast London.
Reports today also say Adebowale's mother sought help from a local mosque because she feared her son was going off the rails after he dropped out of university nine months ago.
Juliet Obasuyi, a Christian probation officer, approached an older neighbour for advice
The neighbour, who did not wish to be named, told The Times that Ms Obasuyi took her son to an imam for help.
Both Adebowale, now 22, and his 28-year-old co-suspect Michael Adebolajo appear to have converted to Islam around the time they left college.
Adebolajo was said to have been popular at his school in Romford, Essex, but Adebowale was bullied at Kidbrooke High School in Greenwich.
A friend who has known him since he was 11 told The Times: “He was one of us ... just normal, nothing completely evil about him at all. He went around preaching Islam, preaching peace though. I must say the whole reform into Islam was quite a sudden change. It was a big shock. But it suited him. It looked like he was doing well.”
Simone Edwards, 22, a close friend of Adebowale’s, said that he converted after being bullied at school. She said: “He was kind of having problems with a couple of gangs. I think he was just looking for somewhere to belong. When he found Islam he finally found a piece of family."
One of Adebowale's neighbours, Magdalene Edwards, told told Channel 4 News: "He was a lovely boy. Very gentle natured, very respectful to elderly people.
"He was angry at a lot of things like a lot of young people are. About a year ago is when I saw him with this whole Muslim dress.
"I said to him are you a Muslim. And he said yes, he's gone that way now. I said just be careful, I'm aware that there are some that ride on the coat tales of Islam and they're really not serving their cause."
Both suspects are still in hospital under guard, and are understood to be in no state to be charged.