An internal review of Garda investigations has found that there were 28 homocide cases in which errors were made and 12 deaths which were misclassified.
The failings include exhibits not being securely stored, statements not being taken, and new lines of inquiry not followed up in a timely manner.
The Garda Review Team is making 21 key recommendations, including major upgrades to the IT system, so that people who are killed are recorded correctly.
Outgoing Chair of the Policing Authority, Josephine Feehily, said it is crucial that the changes are introduced urgently.
"What we are saying right now is that we do not believe that the risks that we identified will have been safely and satisfactorily addressed unless those recommendations are implemented.
"And it's not just the authority, the team led by the Chief Superintendent has said that."