Six officers including the former assistant chief constable of Greater Manchester police will be investigated for misconduct following an inquiry into the death of a man shot by armed police.

Anthony Grainger, 36, was shot through the chest as he sat in a car in the village of Culcheth, Cheshire, in 2012 by an armed police officer known as “Q9”. Detectives believed he and two others were planning to hold up a supermarket and had access to firearms on the evening of 3 March 2012. However, no weapons were found in the red Audi.

Several senior Greater Manchester police (GMP) officers were heavily criticised in a report into the shooting by Judge Thomas Teague QC last year, which concluded after a two-year public inquiry that the force was entirely to blame for his death due to serious failings in its firearms unit.

On Thursday, the Independent Office for Police Conduct (IOPC) announced three new investigations into six GMP officers, including the former assistant chief constable Terry Sweeney.

Sweeney, who was in effect third in command at the force, and two other senior officers – the former superintendent Mark Granby and an unnamed former chief inspector – were under investigation for gross misconduct in relation to their command and control of the operation, the IOPC said. All three officers are now retired.

Another investigation is under way into a now-retired chief inspector and former inspector for gross misconduct over the use of a CS gas canister on the night Grainger died. The weapon, which incapacitates its targets, is not officially approved for use but had been used for at least five years by GMP at the time of the police shooting, the inquiry into Grainger’s death heard.

A third investigation was taking place into a serving GMP officer for misconduct in relation to their management of two firearms officers’ training records, the IOPC said.

All but one of the officers under investigation have retired, meaning no action can be taken against them by GMP. An IOPC spokeswoman said it decided not to name four of the officers “on this occasion” after receiving representations from GMP and the Police Federation, but that it would keep the matter under review.

Amanda Rowe, an IOPC regional director, said the public inquiry had raised further questions about the conduct of some GMP officers before, during, and after the death of Grainger.

She said: “Having these serious matters brought to our attention meant we had to fully consider both Mr Justice Teague QC’s report, and these referrals, before deciding what further actions we may need to take.”

Rowe said GMP had cooperated fully with the investigations.

GMP declined to comment on why it had sought anonymity for four of the six officers under investigation. It said in a statement: “Following the publication of the Anthony Grainger Public Inquiry report in July 2019, Greater Manchester Police sent a further referral to the IOPC. The IOPC are to conduct independent investigations as a result of this referral which will be supported by GMP.”