Lead campaigner Paul May has spoken of Sam’s distress to realise a month after his dad’s death that a photo of his father, taken on the night of Mr Kassahun’s fatal attack, was crucial to his appeal.

In November 2010 Thames Valley Police came to Bullingdon prison to show Sam and Paul photos on Sam’s phone, seized by police when he was arrested nine days after the 2004 murder,

They revealed that contrary to Sam’s belief that he had been with his friend playing football, he had actually been with his father Terry in the George and Vulture pub in Pitfield Street.

Sam’s father had killed himself a month before, due to the stress of the case.

“It was a physical shock to Sam to be shown a photo of his late dad,” said Mr May.

“It was very distressing, not long after Terry’s funeral to be shown that, and to realise this photo was crucially important.

“It placed Sam 1.7 miles from the scene of the murder, shortly before the murder. We also had evidence he had been in the pub, as one of the suspects said he had been there and seen Sam as he was on his way back from the murder scene.”

Sam always maintained he was sure there were photos taken on the night which would show he was with his friend Timmy Harrington with whom who he was playing football. Mr Harrington told police he hadn’t seen Sam, and although he was much less sure in court, the prosecution claimed Sam had concocted a false alibi.

Photos taken on the phone of Mr Harrington proved Sam had met with him that week, but the night after the murder.

Mr May criticised the Met for never carrying out “cell site analysis” on Sam’s mobile phone to find out which phone mast he was nearest at the time of the attack.

What went wrong?

Sam Hallam was nowhere near the scene of the crime, people at the scene said he was not there, he was not captured on CCTV and there was no evidence linking him to the attack on Essayas Kassahun. So just how was Sam Hallam found guilty?

The Crown Prosecution Service’s case was based on evidence from two witnesses who said they were present at the murder and that they had seen Sam take part in the fatal attack.

At the jury trial in 2005, Phoebe Henville said she had seen Sam but she changed her story several times to police and in court.

Bilel Khelfa told police he had seen Sam standing over Mr Kassahun. But he retracted this in court, saying he only named Sam because he had been told by Henville he was involved.

Subsequently the Thames Valley investigation on behalf of the CCRC revealed the ‘‘Sam’’ mentioned by the witnesses was another Sam.

This lead was never followed up by the Met, and the message was never disclosed to Hallam’s lawyers.

As part of the CCRC inquiry, Thames Valley officers interviewed several new witnesses who came forward to say Sam was not involved.