Nineteen people have refused to assist with an independent probe into the role of West Midlands Police after the Hillsborough disaster.
The Independent Police Complaints Commission has contacted 258 officers and staff members who were involved with the force's investigation into the 1989 tragedy, which claimed the lives of 96 Liverpool fans.
A total of 161 statements have been taken so far but 19 individuals have declined to co-operate with the IPCC and nine people have been deemed unable to assist for health reasons, said the watchdog.
The role of West Midlands Police and those who led its investigation into the conduct of South Yorkshire officers in the aftermath of the disaster is one of a number of areas the IPCC is looking at in its largest-ever inquiry into alleged criminality and alleged police misconduct.
A West Midlands Police investigation team was tasked with investigating the conduct of South Yorkshire officers for the initial independent inquiry into the disaster led by Lord Chief Justice Taylor, the Director of Public Prosecutions and the South Yorkshire Coroner.
The IPCC is reviewing and analysing thousands of documents to help establish how that evidence was gathered and then handled, including what was provided to the Director of Public Prosecutions in 1990.
In its latest monthly update into the progress of the probe, the IPCC said it is continuing to liaise with the Crown Prosecution Service about individuals it considers to be suspects.
The IPCC said it has submitted 'substantial evidence-based files'.
A spokesman said: "Our intention remains to submit full files of evidence to the CPS by the turn of the year to enable decisions to be made on whether any individuals should be charged."
In April, an inquest jury concluded the 96 victims of the Hillsborough disaster were unlawfully killed and that blunders by South Yorkshire Police 'caused or contributed to' the disaster at Sheffield Wednesday's stadium in April 1989.
The disaster unfolded at the FA Cup semi final between Nottingham Forest and Liverpool when too many fans were allowed into the stadium - causing a huge crush in the pens at the Leppings Lane end.