Nasiri Moosakhan, 20, had met friends to play football in Plashet Park, near East Ham station, when an argument flared into violence. Shocked families looked on as paramedics battled to save his life.
A post-mortem examination held yesterday gave the cause of death as a stab wound to the heart.
Daud Musafer, 28, told the Standard his cousin - known as Musa - travelled to London from Kunduz province in Afghanistan two years ago following the slaughter of his mother, brother and father. Mr Musafer said: “I received a call and ran to the park.
“My cousin was just lying there, he had a wound in his chest. He lived for about 20 minutes but could not be saved. I cannot believe this has happened in the UK, in London. I told him he would be safe here, in the champion of countries, in the best city. I feel terrible, it’s just a waste. I am heartbroken. He was just in the park to hang out and play sport.”
Mr Musafer added: “Musa was working hard as a builder and a labourer and bettering himself. He loved playing sport, especially basketball. Because his family had been killed I was his closest relative.
“I was like a dad and a brother to him. He was a genuinely good person, he would not hurt anyone. I thought he was safe here - I was wrong.”
The stabbing happened at about 4pm on Sunday near the basketball court at the Shrewsbury Road entrance to the park. It is yards from Plashet secondary school for girls.
A friend who was with Mr Moosakhan, of East Ham, at the time said: “It was a stupid argument. It was over in a second... it was horrible.
“Musa was a good man. He worked hard and was very friendly. I can’t believe he has gone.”
Families enjoying the sunny weather fled the park in panic. One father said: “One minute it was a lovely peaceful sunny day and then we were running for the exit. We were in total shock.” A police cordon remained around the scene yesterday.
Detective Chief Inspector Jamie Piscopo, leading the police investigation, said: “There are still outstanding suspects. This was a violent attack on a young man which happened in the middle of the afternoon in a busy park, and I would ask anyone who saw the incident to come forward and speak to us.”
A 16-year-old boy has been charged with murder and is due to appear at Barkingside youth court today.
Witnesses are urged to call the Met’s Homicide and Major Crime Command on 020 8345 3715 or Crimestoppers on 0800 555111.