The biggest ever independent investigation into police wrongdoing is to be carried out following a damning report into the Hillsborough disaster.
The IPCC police watchdog and director of public prosecutions have announced they will both launch inquiries into possible crimes committed by police.
The IPCC said both serving and former officers would be investigated over the deaths of 96 Liverpool fans in 1989.
The Hillsborough Family Support Group said it was "too good to be true".
The Director of Public Prosecutions Keir Starmer will review evidence relating to how the 96 fans died, which could lead to charges of manslaughter through gross negligence.
Meanwhile, the IPCC said it would look at whether there was a criminal cover-up by South Yorkshire Police of failings by the force.
A "large number" of current and former officers now face investigation over claims made in a report on the Hillsborough disaster, the IPCC said.
The Independent Hillsborough Panel Report last month revealed 164 police statements were altered - 116 of them to remove or change negative comments about the policing of the FA Cup semi-final between Liverpool and Nottingham Forest at the Sheffield stadium.
It said police and emergency services had made "strenuous attempts" to deflect the blame for the disaster on to fans.
The panel also found that 41 of the 96 who died had the "potential to survive" and calls have been made for fresh inquests.
The Attorney General is currently considering whether to apply to the High Court for the original inquest verdicts to be quashed.
Deborah Glass, deputy chair of the Independent Police Complaints Commission (IPCC), said "without a shadow of a doubt" it would be the biggest ever investigation carried out into police behaviour in the UK.
Both South Yorkshire Police, which dealt with the tragedy, and West Midlands Police, which investigated how South Yorkshire handled the disaster, will come under scrutiny.
Sir Norman Bettison, currently chief constable of West Yorkshire, has also been referred to the IPCC over allegations that he provided misleading information after the tragedy.
It was revealed that he is under investigation for allegations that he "attempted to influence the decision-making process of the West Yorkshire Police Authority in connection with the referral that they had made," Ms Glass said.
A West Yorkshire Police spokesperson said: "Sir Norman Bettison has consistently made the point since 15 September, three days after the report was published, that these were matters that needed to be investigated formally and fairly by the IPCC.
"He is on record as saying he is keen to co-operate with the IPCC inquiry, but now that has been launched, he has nothing further to add."
David Crompton, the chief constable of South Yorkshire, and Chris Sims, who heads West Midlands Police, both said their forces would co-operate fully with the IPCC investigation.
The panel disclosed potential crimes committed before, during and after the disaster, said the IPCC.
The parallel investigations will cover possible offences of manslaughter, perverting the course of justice by changing police statements, perjury by officers who gave evidence on oath, perverting the course of justice by misleading journalists and misconduct in public office.
Claims that officers questioned bereaved next of kin about their loved ones' alcohol consumption, carried out alcohol testing and checked the police national computer to find information about the dead and injured will be investigated.
Responding to the news of the inquiries, Deputy Prime Minister Nick Clegg said everything the families of Hillsborough victims had said was justified and added: "You need truth, then you need to use the truth against people who did some very bad and wrong things."
Liverpool FC said the inquiries were "another significant step forward in the campaign for justice for Hillsborough families and survivors".
Sue Roberts, the secretary of the Hillsborough Family Support Group (HFSG), said: "I just hope it all goes through, it seems too good to be true at the moment.
"I haven't heard the full detail yet but it just seems as though everything is going in our favour so fingers crossed it continues in that vein for a change."
Margaret Aspinall, the group's chairwoman, who lost her son James in the disaster, said she believed "all the families would be quite pleased" with the development.
She said: "We have more waiting ahead of us but we have had 23 years of waiting."
The Mayor of Liverpool Joe Anderson said: "The families have waited 23 years to obtain justice and this announcement sets the wheels in motion at long last.
"I sincerely hope that no stone will be left unturned in delivering the outcome that the families deserve."