Greater Manchester Police is being investigated over evidence it gave following the death of PC Ian Terry, the IPCC has said. The officer was shot dead in a botched training exercise in June 2008.
No officers have ever faced criminal charges over the death of Mr Terry, a father-of-two, although an inquest in 2010 found he was unlawfully killed.
Two officers were found guilty of gross misconduct at internal disciplinary hearings, while a third retired before proceedings could be held.
An IPCC spokesman said a new investigation had been launched into the actions of officers following Mr Terry's death and the evidence they provided.
He said: "Some of the allegations are still being assessed at this time to determine whether or not they warrant investigation.
"However, the IPCC has commenced an investigation looking at evidence given by a number of officers to the IPCC, to the inquest after Pc Terry's death, and to the subsequent Health and Safety Executive (HSE) crown court trial."