Potential evidence in the controversial killing of a Co Armagh man was removed from Special Branch offices, a Police Ombudsman report is expected to conclude.
Neil McConville (21) pictured, from Bleary died in hospital after police shot him when his car allegedly crashed through a checkpoint near Lisburn in April 2003.
He was the first person in the north to be shot dead by police since the 1992 killing of Pearse Jordan (23) in west Belfast.
It remains the only such case involving the PSNI.
However, a report due to be published by Police Ombudsman Nuala O'Loan is expected to state that evidence relating to the case had been removed from Special Branch offices before her investigators could view it.
Some officers were reported to have been "non-cooperative, obstructive and difficult" when questioned by Mrs O'Loan's detectives.
On the day Mr McConville was killed undercover officers and a helicopter had monitored the movements of his car in Belfast, where it was alleged that a gun was being picked up.
As the red Vauxhall Cavalier carrying Mr McConville and a passenger left the city, seven cars carrying 21 undercover police officers followed.
At 6.55pm police claimed that they ordered his car to stop.
It is alleged the Cavalier then swerved into a police vehicle, spun and ended sideways on the road.
Police then smashed the driver and passenger windows and it was claimed the 21-year-old reversed his car, hitting an officer.
He was hit by three shots fired by a second officer, while the second man in the vehicle was also hit. The passenger was later charged with possession of a sawn-off shotgun.
Mrs O'Loan is expected to conclude that police withheld evidence after all material relating to the killing, including a computer hard drive, was removed from Special Branch offices before investigators had arrived.
It is understood that police claimed the removal of evidence was the result of "human error".
Mrs O'Loan's report is expected to state that officers overseeing the security operation were "non-cooperative, obstructive and difficult" when questioned.
Criticisms are expected to include a failure to issue clear commands to special support units involved in the incident.
A senior officer in charge of the operation, identified as Superintendent 'B', has been accused of failing to keep any verifiable records of the operation in the control room. There are also concerns over his accounts of events.
The Ombudsman is understood to have prepared files to be delivered to the Public Prosecution Service.