A senior officer is being investigated for gross misconduct by the police watchdog after four Vietnamese men were found dead following a mill fire.
The Independent Office for Police Conduct (IOPC) said two other officers were being investigated for misconduct.
It said it was assessing "a potential breach of professional standards".
The four men's remains were only found by demolition workers in July 2022, two months after the blaze at Bismark House Mill in Oldham, Greater Manchester.
Emergency services initially thought no-one had been in the property when the fire broke out on 7 May.
The IOPC investigation into the conduct of the three officers – regarding contact with the dead men's families – started in September following a referral from Greater Manchester Police (GMP).
An IOPC spokesman added that the senior GMP officer had been served with a notice that they were being investigated for "a potential breach of professional standards that could amount to gross misconduct".
He said: "It relates to an allegation that the officer failed to disclose relevant information regarding a criminal investigation into the recovery of the bodies."
Two other officers have also received a notice that they are being investigated for "a potential breach of professional standards that could amount to misconduct".
"This relates to the extent of checks and action that was taken following information they received," the IOPC spokesman said.
He said statements and interviews with some of the officers had been obtained and more lines of inquiry were being progressed.
While notices are issued when there is an indication of misconduct, they do not automatically mean misconduct proceedings will follow, he added.
GMP said none of the officers in question had been suspended.
The remains of Cuong Van Chu, Uoc Van Nguyen, Duong Van Nguyen and Nam Thanh Le were recently returned to their families in Vietnam.
Four people were arrested on suspicion of manslaughter and remain on bail.
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