Twenty-two people have now been identified as suspects by two ongoing investigations into the Hillsborough disaster, including some who were not police officers.
Yesterday, the Independent Police Complaints Commission (IPCC) confirmed 13 retired or serving police officers were now being regarded as suspects as part of its inquiry into the aftermath of the 1989 tragedy in Sheffield.
Today, the IPCC said Operation Resolve - the wider criminal investigation into the disaster - has also identified 13 people "who fall within the suspect category".
It said six of these are retired police officers and seven worked for other, non-police organisations.
As the commission said four of those identified are being treated as suspects by both investigations, the total number of people being treated in this manner is now 22.
The IPCC confirmed that some of the retired or serving police officers being treated as suspects in its own inquiry are being interviewed on suspicion of manslaughter.
In its latest bulletin about the Hillsborough investigation, the commission said: " As part of the IPCC's ongoing investigations we have begun interviewing people as suspects.
"Thirteen retired and serving police officers have been identified as suspects so far. These are being interviewed under criminal caution on suspicion of a range of criminal offences.
"Some officers have been interviewed on suspicion of perverting the course of justice and misconduct in a public office, while others have been interviewed on suspicion of manslaughter. Four of those interviewed were subject to joint interviews with Operation Resolve."
The IPCC's inquiry - the biggest it has ever undertaken - covers the actions of the police in the aftermath of the crush at Hillsborough stadium in Sheffield in April 1989, which left 96 Liverpool fans dead.
The investigation was announced after the commission reviewed the report of the Hillsborough Independent Panel, which undercovered a huge amount of new evidence about what happened during and after the tragedy.
It is examining allegations including those surrounding amendments to police statements, the actions of the police officers after the disaster and the role of West Midlands Police, which investigated what happened at the time.
Operation Resolve, under the command of assistant commissioner Jon Stoddart, the retired chief constable of Durham Police, is a new, wider-ranging criminal investigation into the disaster.
The IPCC said today: " I n the last two weeks, Operation Resolve has also commenced interviews with those individuals who have been identified as suspects and these interviews are taking place under criminal caution.
"To date, Operation Resolve has identified 13 individuals who fall within the suspect category; four of these are of the joint interviews with the IPCC. Six of these individuals are retired police officers, the remaining seven are from other organisations."
New inquests into the 96 deaths are due to begin in Warrington on Monday and, in relation to this latest information, the IPCC said: " As this is a criminal investigation, we do not intend on disclosing publicly the names of the individuals who are regarded as suspects.
"We will, however, provide these names to the coroner should he request them and we have made this clear in our latest update to him."
In its latest update, the IPCC said 1,700 witnesses had now come forward, including 400 who had never given an account before.
In relation to the controversial issue, highlighted by the Hillsborough Independent Panel, of police officers changing their statements about the tragedy, the commission said eight further suspected examples had been identified.
It said it had now identified a total of 251 accounts " which are suspected of being subject to amendments".
Of these 251 officers, 24 are dead, 12 have been deemed unfit for interview at this time and 13 have refused to be interviewed, the IPCC said.
IPCC Deputy chair Rachel Cerfontyne said: " We have moved into the phase of conducting suspect interviews.
"These are interviews under criminal caution of individuals who are suspected of committing offences such as perverting the course of justice, misconduct in a public office and manslaughter.
" These are the first tranche of individuals we have deemed suspects. I do not expect them to be the last."
Ms Cerfontyne said the commission was continuing to look at allegations from some families of those who died that they had been subject to police surveillance.
"We have also been conducting further work around the allegations of surveillance we have received," she said.
"We have received one specific allegation against a named police force - West Midlands Police - and we will be investigating this as part of our independent investigation into the aftermath of the disaster."