Video evidence shot by police during the Hillsborough disaster may have been tampered with, a coroner heard.
Pete Weatherby QC, representing a group of victims' families, told a pre-inquest hearing that the handheld footage might have been edited before it was handed over to an expert.
He asked coroner Lord Justice John Goldring for an audiovisual specialist to be among those giving evidence at new inquests into the 96 victims' deaths next year to ensure that the best available footage is shown to the jury.
The hearing was also told that the BBC had agreed to release previously unseen footage from the disaster and extended interviews with witnesses.
Earlier, counsel to the inquests Christina Lambert QC revealed that a report into whether lives could have been saved if emergency services had acted differently would be considered.
The inclusion of such evidence represents a major shift from the original 1991 inquests, quashed in December, which established that no victims could have survived if they sustained injuries before a 3.15pm cut-off point.
Andrew O'Connor, representing the Independent Police Complaints commission (IPCC), said its investigations had uncovered an additional 74 altered police statements.
He told the coroner that the watchdog was in the process of interviewing all 220 living officers suspected of doctoring their reports.
And Michael Mansfield QC, representing a large group of victims' families, reiterated a petition for jurors to be taken to Hillsborough during the inquests.
It came after Lord Justice Goldring told the packed-out pre-inquest hearing of his intention for the inquests due to be held in Warrington, Cheshire, to go ahead on March 31 as scheduled.
He said: "I certainly remain committed to that date and it is partly for that reason that I have sought, obviously through those who are helping me, to drive those investigations forward as much as I can.
"I shall not cease, so that it is absolutely clear, to seek to drive these investigations onwards as much as I conceivably can."
Relatives attending the hearing at a central London hotel told reporters that after waiting 25 years for justice they would be opposed to any delays.
There was anger among them as Christopher Daw QC, speaking for retired chief superintendents Terry Wain and Donald Denton, asked the coroner for them to be represented as interested persons at the inquests.
When Mr Daw pointed out that both men are now in their 70s there was a sigh from the public gallery, with one woman saying out loud: "What about the parents who are in their 70s? Disgrace."
Mr Daw was cut short by the coroner as he argued that there had been no "cover up" by his clients, who were charged by South Yorkshire Police to conduct internal investigations following the tragedy.
Lord Justice Goldring said: "I don't think this is the time to go into a speech about that."
The coroner granted both retired officers' application to be represented separately at the inquests.
Richard Whittam QC, representing the Director of Public Prosecutions, told the hearing that a beefed up team was considering whether criminal charges should be brought in relation to the disaster.
"Nobody should doubt the intellectual rigour that will be brought by the Director of Public Prosecutions to evidence considered by the Crown Prosecution Service," he said.
"There is a dedicated team looking at prosecutions should they be appropriate and lawful.
"Should there be sufficient evidence to bring prosecutions it is likely that any and every legal challenge will be met along the way.
"The Director is clear that nothing should be done which is a bar to future prosecutions."
Britain's worst ever sporting disaster happened at Sheffield's Hillsborough stadium on April 15 1989 during Liverpool's FA Cup semi-final against Nottingham Forest as thousands of fans were crushed on the ground's Leppings Lane terrace.
Verdicts of accidental death from the original Hillsborough inquest in March 1991 were quashed last December.
The action was taken after the Hillsborough Independent Panel studied thousands of documents and reported that there had been a huge cover-up of what happened at Hillsborough and its aftermath.
After the hearing, a BBC spokeswoman said they had already released untransmitted on several occasions.
She added: " The BBC has already disclosed to both the Coroner and Operation Resolve, which is staffed by Greater Manchester Police, the BBC's untransmitted footage filmed at the stadium on the day.
"Our records indicate that this footage was all disclosed to West Midlands Police on behalf of the Taylor Inquiry in 1989, to the Home Office who requested it on behalf of Lord Justice Stuart-Smith's Hillsborough Scrutiny in 1997 and that on a number of occasions it was also disclosed to the relatives/representatives of victims where it had been requested."