A television investigation has found that crucial evidence from the 1989 Hillsborough disaster was undermined wrongly at the original inquest.
Off-duty Merseyside Police constable Derek Bruder has always maintained that he tried to treat Liverpool fan Kevin Williams after 3.15pm - the time after which coroner Stefan Popper said none of the victims could have survived.
Bruder's evidence was dismissed as unreliable at the 1991 inquest, but analysis on unbroadcast television footage from the BBC's Panorama programme has found his account to be true. The programme will be broadcast by the BBC on Monday evening.
Ninety-six Liverpool supporters died in a crush at the FA Cup semi-final against Nottingham Forest at Sheffield Wednesday's ground on April 15, 1989.
In the original inquest, Popper ruled that none of those who died could have been saved after 3.15pm, giving verdicts of accidental death.
Those verdicts were quashed at the High Court in December 2012 after an independent report established that 41 of the victims could have been saved. Fresh inquests will be held early next year.
The Hillsborough Independent Panel report, which exonerated Liverpool fans of any blame for the disaster, laid bare the extent to which the police and emergency services had attempted to cover up their own culpability for the tragedy.
It backed the long-held belief, stated by campaign groups, that the original inquest verdicts had prevented a proper investigation into events at Hillsborough.
Williams, who was 15 when he died, was one of those who it is believed could have been saved after 3.15pm.
His mother Anne campaigned for new inquests for more than two decades before her own death from cancer in April this year.
Footage analysed by Panorama showed Bruder, an off-duty officer with Merseyside Police, trying to resuscitate her son at around 3.35pm.
In an interview with Panorama shortly before her death, she said he had told her how he had tried to help, adding: "He told me then what he'd done for Kevin. and I said: 'Was my son alive?'
"And he said: 'Well, if you say finding a pulse with the first two fingers... if that means he was alive, then he was alive.'"
Bruder said that an ambulance was driving onto the pitch past him as he attempted to treat Williams, but he was not called to give evidence at the original inquest.
Instead, his evidence was outlined by a West Midlands police officer, who mentioned only two ambulances going into the ground, both before Williams was carried to the spot where Bruder attempted to save him. Bruder's evidence was considered unreliable as a result.
But footage analysed by Panorama showed a third ambulance arrived on the pitch after 3.30pm.
Tony Edwards, who was inside the third ambulance, said the West Midlands officers investigating the disaster at the time knew this.
He told the BBC: "They had a video set up, they had photographs and they had laid out photographs as well and it was them who said to me: 'I want to show you your vehicle coming on the pitch at 3.35pm.'"
Bruder told Panorama he had made a complaint to the Independent Police Complaints Commission (IPCC), the UK's police watchdog, about how his evidence had been handled.
West Midlands Police told the BBC it would co-operate with the IPCC and could not comment while inquiries continued.
Yorkshire Ambulance Service NHS Trust said it would co-operate with any new legal inquiries.