The Law Enforcement Conduct Commission has analysed 29 investigations into critical incidents - which involve a police operation that results in death or serious injury - that began before the commission formed in July 2017.

It found unreasonable delays by police in finalising 27 per cent (8) of them.

However guidelines do not provide police with a clear indication of time frames within which an investigation should be completed, the study found.

It's important police address unnecessary delays as they may result in adverse effects, "not the least of which is the distress endured by the families of the deceased and injured and of the officers involved in these incidents", it says.

The LECC also found some key critical incident investigation records could not be located in the NSW Police investigations management system, which impacted on its ability to properly assess compliance.

The review also found "very low levels" of compliance by police in conducting mandatory alcohol testing within two hours of incidents occurring and preparing interim reports before the end of coronial inquests - both required under critical incident guidelines.

The commission is "particularly concerned" by the inadequacy of a form used to identify and keep account of the ways conflicts of interest are managed in critical incident investigations.

Only 19-of-the 29 investigations contained a conflict of interest form and of these, only 11 complied with guidelines.

"In many instances, the way that conflicts of interest were documented did not clearly identify what the conflicts were, nor what treatment strategies would be implemented to avoid any such conflict, actual or perceived, impacting on the conduct of the investigation," the report concluded.

The commission has made a number of recommendations to help police improve compliance, which are supported by NSW Police.

Australian Associated Press