Files of evidence are expected to be handed over to the Crown Prosecution Service by the end of the year for decisions on whether anyone should be prosecuted over the Hillsborough disaster.
There are two investigation teams looking at the 1989 disaster in Sheffield which claimed the lives of 96 football fans - one looking at the causes of the disaster including the events on the day and those leading up to it and the other looking into police actions in the aftermath of the Hillsborough disaster.
The Independent Police Complaints Commission, which is considering offences including perverting the course of justice, perjury, and misconduct in a public office, said both investigation teams are due to pass on full files of evidence to the CPS by the end of the year.
Deputy chairman, Rachel Cerfontyne, said: "Both investigation teams have started to disclose evidence to the Crown Prosecution Service.
"This work is being done to prepare for charging decisions, which will be made by the CPS once the criminal investigations are complete and full files of evidence have been provided at the turn of this year."
In its monthly update, published yesterday, the IPCC said it plans to pursue uncooperative witnesses if it believes they can 'significantly enhance' its probe into the Hillsborough disaster.
Earlier this month it said 19 individuals had declined provide statements to investigators examining the role of West Midlands Police after the 1989 tragedy.
The force was brought in to investigate the conduct of South Yorkshire officers for the initial independent inquiry into the disaster.
Ms Cerfontyne said the majority of those approached to help with the investigations had done so, with more than 13,000 statements recorded by both teams.
She said: "This has helped us to develop an in-depth working knowledge of what happened at Hillsborough. If we believe any of those who have declined could significantly enhance the investigations, we will continue to persuade them to engage with us.
"National legislation means that no investigation has the power to force witnesses, whether they are police officers or members of the public, to give accounts."
In April, an inquest concluded the 96 victims were unlawfully killed and that blunders by South Yorkshire Police 'caused or contributed to' the disaster at Sheffield Wednesday's stadium at an FA Cup semi-final between Liverpool and Nottingham Forest.