Sam Hallam, who was convicted of the murder of trainee chef Essayas Kassahun seven years ago, has been freed by the Court of Appeal.

Kassahun, 21, was murdered by a group of youths wielding baseball bats on the St. Luke's estate in Clerkenwell, London.

Hallam, now 24, had always insisted he was not at the scene, but was instead playing football with a friend half a mile away. His mother, Wendy Cohen, has waged a seven year campaign attesting his innocence, attracting the support of celebrities including Ray Winstone. Hallam's father committed suicide while his son was in prison.

Hallam's first appeal was quashed in 2007, but the case was reviewed by the Criminal Cases Review Commission and passed to Thames Valley police who picked up the investigation from the Metropolitan police. New evidence then came to light which cast doubt on the original conviction.

Two witnesses claimed to have see Hallam at the scene of the murder near Old Street, where a mob of youths attacked Kassahun. But one later withdrew her evidence telling the court: “I was just looking for someone on the spot to blame.”

Other crucial evidence, such as mobile phone data, was overlooked.

Sam Hallam's mother, Wendy Cohen. Photograph: Getty Images

In a statement outside the court, Hallam said:

I don't want anyone else ever to suffer what I've been through since 2004.

The identification evidence against me was so unreliable that it should never have been put to the jury...justice has long been denied to me but it has now finally prevailed.

The hearing was due to last two days but Hallam was told he was to be freed immediately on bail yesterday. The prosecution indicated they would not oppose his appeal against conviction. Hallam sat in the public gallery today with his mother to hear the judges give their reasons for overturning the sentence.

He had been due to serve a sentence of 12 years in prison. One other person, Bullabeck Ringblong, was also convicted of the murder.