A prisoner was left “hysterical, crying and screaming” as his friend lay dying from a deep stab wound in his chest, a former inmate has said.
And, when told 21-year-old Jamal Mahmoud was dead, one of his alleged killers "just shrugged it off", jurors at the Old Bailey were told.
Cisse Ewango was giving evidence in the trial of three men accused of knifing to death the young father at Pentonville Prison in October.
He said officers trying to save Mr Mahmoud's life were performing CPR before one of the alleged killers, Basana Kimbembi, stamped on his head.
Mr Ewango, who stepped in to calm the situation, said officers then turned the motionless Mr Mahmoud onto his back, revealing a "big gash" in the middle of his torso.
Mr Mahmoud, nicknamed Kaos, led a gang known as The Somalis and was allegedly killed in a battle over the lucrative contraband route on G Wing.
As the alarm sounded on the afternoon of the killing, Mr Ewango said he saw one of The Somali gang "hysterical, crying and screaming".
He said: "As I get nearer, I see Kaos laying on the floor on the landing near the stairs.
"He was passed out, not moving, his eyes and mouth are open."
Then, Kimembi jumped from the stairs and "violently attacked" Mr Mahmoud by "stamping on his head", he said.
Officers then started to "trade blows" with Kimbembi, before he and another inmate stepped in to break them apart.
Mr Ewango added: "Other officers arrived and turned Kaos onto his back and that's when we saw the wound.
"After that I walked back to my cell and Kimbembi was there. He's dressed differently, wearing my green trousers and a black T-shirt.
"I said 'that guy don't look like he's alive, he's gone'.
Prosecutor Mark Heywood QC asked: "What, if anything, did he say to that?"
Mr Ewango said: "He just shrugged it off," and then denied knifing him.
Instead Kimbembi said he was busy fighting another Somali boy known as "Jimmy", and had stabbed him in the "leg or buttocks", Mr Ewango said.
It emerged during the hearing that Mr Ewango knew Mr Mahmoud from outside prison as a passing acquaintance.
Cross-examining, Michael Holland QC, suggested he was influenced by a fear of retribution from the Get Money Gangsters (GMG) - of which Mr Mahmoud was a member.
Mr Holland said: "Those who are members of a gang can't only threaten inside prison but can take action outside prison against their nearest and dearest if need be.
"Their activities include drug supplying, murder, guns, knives.
"Would you agree that crossing senior members of the GMG isn't something someone who knew their reputation would want to do?"
Mr Ewango agreed if he was seen to be helping Kimbembi with his police statements he could potentially make himself a target of the gang.
But, he added: "I'm a big enough man to defend myself from anyone."
Kimbembi, 35, Joshua Ratner, 27, and Robert Butler, 31 deny murder as well as wounding Mr Mahmoud's associate Mohammed Ali with intent to cause him grievous bodily harm.
Court reporting by Press Association
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here