The PSNI is to suspend investigations into cases from the Troubles and redeploy personnel in response to the coronavirus crisis.
The move will free up about 70 officers and staff in its Legacy Investigations Branch.
Chief Constable Simon Byrne accepted it would cause "distress" to victims' families, but said it was a temporary measure.
He added the staff would be switched to support "critical policing functions".
The branch is dealing with more than 1,100 unresolved cases, covering more than 1,400 killings over three decades.
Mr Byrne made the announcement in a video message posted on social media.
An update on temporary changes to @PoliceServiceNI operations as part of the response to #COVID19, the service will continually update @NIPolicingBoard on our procedures and work with @PONIPressOffice to enhance public confidence. Please #StayHomeStaySafehttps://t.co/cpvmKqHbxG— Simon Byrne (@ChiefConPSNI) March 31, 2020
He also said that in agreement with the Policing Board, the PSNI would begin using spit and bite guards to protect officers in public.
The PSNI has been the only UK police service not to use them before now.
Made of mesh and plastic, they can be placed over the head of an individual to prevent them coughing on, or spitting and biting officers.
In recent days there have been at least 20 "cough attacks" on officers by people claiming to have Covid-19.
Last week it was announced they could be used in custody suites in police stations.
But now their use is to be expanded for officers responding to situations in public were coronavirus might be involved.
Mr Byrne said their use would end with the Covid-19 crisis, pending further discussions with the board.
Amnesty International in Northern Ireland recently cautioned against their use, claiming the guards could restrict breathing.
Mr Byrne said their use would be videoed "where possible" and "the circumstances referred to the Police Ombudsman".