Police officers involved in the Hillsborough disaster are being questioned as suspects for the first time.
Twelve retired police officers and one serving officer are being interviewed.
Elevenhave already been questioned under caution about a range of offences - including manslaughter, misconduct or perverting the course of justice.
In four days time, new inquests into the deaths are due to begin in Warrington. No one has ever been charged over the disaster.
ITV News Correspondent Damon Green reports:
Thirteen retired or serving police officers have been identified as "suspects" in the investigation into the Hillsborough disaster, the IPCC has said.
11 of these had already been interviewed under caution relating to the offences, which include manslaughter, misconduct in a public office, and perverting the course of justice.
A spokesman said the other two would be interviewed in the near future.
The police watchdog - The Independent Police Complaints Commission - say they have identified a total of 13 individuals - 12 former and one serving police officer - as suspects in their investigation into the Hillsborough disaster.
The suspected offences include manslaughter, perverting the course of justice, and misconduct in a public office. Four of those identified are also of interest to the criminal inquiry into the disaster, the IPCC said.
We've identified 12 retired police officers & 1 serving as suspects in our Hillsborough investigation. 4 are also of interest to Op Resolve
Hillsorough investigation: Suspected offences include perverting the course of justice, misconduct in a public office and manslaughter
Lawyers at the inquests into the deaths of 96 people in the Hillsborough disaster have expressed their "considerable regret" for a delay in providing pathology reports to the families of the deceased.
At a preliminary hearing today, counsel to the inquests Christina Lambert QC acknowledged that it was an "extremely difficult and tense time" for the families as the coroner, Lord Justice Goldring, was asked to delay part of the hearing, which are due to start on Monday.
Judy Khan QC, representing 74 families, asked the coroner for a three week break so the families could consider the late pathology reports.
Ms Khan asked for this to take place after the opening statements from the coroner and the families, which are due to start next week after a jury has been selected.
The coroner agreed to allow a delay but said he wanted lawyers at the inquest to liaise on how long this should be.
He agreed that this will take place after his opening statement and after the background "pen portraits" of all the victims which are to be presented by the families after the coroner has finished his opening.
These are scheduled to be completed by April 29.
Ms Lambert said: "It is matter of considerable regret that we were not able to provide the families with the pathology reports earlier.
"We recognise fully this has placed an emotional burden on families at an extremely difficult and tense time for them."
All English professional matches over the weekend of April 11-14 will kick off seven minutes later than scheduled to mark the 25th anniversary of the Hillsborough stadium disaster.
The tribute will take place in all games in the Premier League, Football League, Football Conference and FA Cup. There will be a minute's silence before each match kicks off.
It has been organised as "a mark of respect and remembrance" for the 96 people who lost their lives in the disaster on April 15, 1989.
That match, the FA Cup semi-final between Liverpool and Nottingham Forest, was ended six minutes after kick-off, at 3:06pm.
Home Secretary Theresa May will look into a police force's "disgusting slurs" that drunkenness played a part in the deaths of 96 Liverpool fans in the Hillsborough disaster.
Labour frontbencher Andy Burnham expressed his outrage that South Yorkshire Police are "re-running slurs about alcohol" after reports that senior officers will argue that drunkenness contributed significantly to the tragedy when new inquests open next month.
Mrs May said she was prepared to look into the matter after the shadow health secretary pointed out that the 1989 Taylor report and the 2012 HillsboroughIndependent Panel found that alcohol did not play a major part in the disaster.
The inquests are due to begin in Warrington, Cheshire, on March 31 - nearly 25 years on from the disaster at Sheffield's Hillsborough stadium.
The tragedy - Britain's worst sporting disaster - happened on April 15, 1989 during Liverpool's FA Cup semi-final against Nottingham Forest as thousands of fans were crushed on the ground's Lepping Lane terrace.
Verdicts of accidental death from the original Hillsborough inquest in March 1991 were quashed in December 2012.
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.
It has emerged that 1600 people have now given evidence to two investigations into police conduct in the aftermath of the Hillsborough disaster.
The Independent Police Complaints Commission and criminal lawyers are both looking into the way police behaved after 96 people died at the stadium in 1989.
Today the Home Secretary, Theresa May, said 250 of the witnesses who have come forward have never given evidence before:
The police watchdog will pursue concerns that families of Hillsborough victims were spied on if evidence emerges, Home Secretary Theresa May has said.
Mrs May said the Independent Police Complaints Commission (IPCC) had received no formal complaint or allegation but was aware of the concerns.
The IPCC is conducting its biggest-ever investigation which focuses largely on police actions after the tragedy that left 96 football fans dead, MPs heard.
Mrs May added police forces could be ordered to release all documents connected to the disaster if investigators encounter problems.
Addressing the concerns over undercover surveillance of families, Mrs May told MPs: "No formal complaint or allegation has been made to the IPCC but it is aware of the concerns and it is considering how it should best address those concerns.
"Of course, it is reviewing the material in relation to Hillsborough so if they discover any evidence in their investigation that suggests surveillance may have taken place of the sort that's been suggested then they will of course pursue that evidence."
Football League clubs have called for the Government to review the rule that means stadiums in the Championship must be all-seater but face opposition from Hillsborough campaigners.
A majority of the 72 clubs have voted for League chiefs to approach the sports minister to ask for a review and that rail seating - where there is a safety barrier on every row and seats can be locked in an upright position - be permitted.
All-seater stadiums in the Championship and Premier League became law after the 1989 Hillsborough disaster, and Margaret Aspinall of the Hillsborough Family Support Group said they still opposed any reversion to standing areas.
Hillsborough survivors have spoken of how they were "scared and intimidated" by officers from the force tasked to independently investigate the football disaster.
The new investigation into the tragedy, which killed 96 Liverpool fans in 1989, has already uncovered a mass of statements given by police officers on the day that were doctored by South Yorkshire Police.
A subsequent inquiry carried out by West Midlands Police into the handling of Hillsborough by their counterparts in South Yorkshire has also become the focus for possible criminal conduct after the Independent Police Complaints Commission (IPCC) found "differences" in statements taken from fans.
The BBC's Newsnight has spoken to survivors who have also spoken of being mistreated by officers from West Midlands Police and questioned how officers took their statements.
One of them, Nick Braley, said that when he told West Midlands officers that he thought South Yorkshire police failings had caused the disaster, he was told he could face prosecution.
Around 12,000 people spoke to West Midlands Police as part of its inquiry.
Analysis shows statements taken by West Midlands Police officers from supporters are not the same as the details given by the same individuals in questionnaires they had completed earlier.
Its investigation formed the basis of Lord Taylor's judicial inquiry into the disaster, the subsequent decision not to prosecute individuals, and the flawed inquests whose verdicts were quashed in 2012.
The IPCC said last year it wants to hear from anyone who gave evidence to West Midlands Police either in writing, via telephone or in face-to-face interviews.
Last September a damning report by the Hillsborough Independent Panel found that South Yorkshire Police orchestrated a cover-up of events, falsified documents and blamed innocent supporters for the tragedy.
It also raised "serious questions" over the work done by the West Midlands police force.
The report led to a public apology by Prime Minister David Cameron, the quashing of the original inquest verdicts, the resignation of a chief constable and the launch of two further investigations into the disaster, with criminal prosecutions of individuals and corporate bodies not ruled out.
Last month IPCC investigators said they were close to "identifying and interviewing people as suspects".