A teenage stab victim was hit with a hammer as a friend was calling 999 for an ambulance, a court has heard.
Cemeren Yilmaz, 16, known as Gem, died following two cardiac arrests and brain damage after the attack in the Ashmead Road area of Bedford in September.
Aaron Miller, 20, of Tavistock Street, Bedford, and three 15-year-olds, who cannot be named, all deny murder.
Gem's 16-year-old friend told the court that two of the defendants hit him with a hammer after he was stabbed.
Earlier, St Albans Crown Court heard the background to the case concerned "hostility" between two rival Bedford gangs.
Prosecutor Stuart Trimmer QC told the jury Cemeren, who was linked to a gang, met up with friends and, after an earlier confrontation, was chased by two youths from a rival gang.
As he lay on the ground, he was stabbed with a large knife which caused a severe injury to his kidney.
Two other members of the rival gang are then alleged to have delivered blows to his head and face with a hammer, and a combination of the two attacks caused the boy's death.
Giving evidence, Cemeren's friend said he saw Mr Miller punching the victim and saw a "knife drop on the floor" which was picked up.
"Then it all happened quickly. I saw Cemeren on the grass just lying down," he said.
"I could see the cut on his head. He was saying stuff like 'I think I am dying'."
The friend told the court he did not see who had delivered the fatal wound.
In a 999 call, which was played to the jury, the friend was heard to say: "Some people ran up to him and stabbed him."
He then told the jury that when two of the other defendants hit Cemeren with a hammer, he "didn't try to stop it".
"They had a weapon and I had nothing. I was right next to him," he said.
He said the attackers ran off and an ambulance arrived.
Cemeren, from Harrold, died in hospital the following day.
The trial continues.