Copies of thousands of DNA and fingerprint samples are to be made to help with future investigations into crimes committed during the Troubles.
Under new legislation coming in this October, police are required to delete the genetic information of people who do not have convictions.
However, the justice minister said some samples would be copied to help the new Historical Investigations Unit (HIU).
The unit was set up under the Stormont House Agreement last December.
"Roughly half of the 33,000 samples which would otherwise have to be destroyed will be copied," David Ford said.
"It's clear that some of the data which is currently held might be of relevance to the HIU.
"There's little point in setting up a new investigative unit and then removing its opportunities."
He said the actual samples that are held for the police will be destroyed, but digital copies will be made that will be accessible only by the HIU.
Mr Ford said he believed this was proportionate and met EU requirements.
"What we've had to do is balance two provisions under the European Convention of Human Rights," he said.
"The article eight provision - the right to a private life, which is the basis under which data is to be destroyed from those who haven't been convicted or those who have been convicted of minor offences after a certain period of time, against the article two obligations that we have to investigate in order to protect life.
"I believe that this is the appropriate balance between those two measures."
The DUP's Jeffrey Donaldson said the justice minister had made the right decision.
"Article two of the European Convention requires the state to protect human life and I believe that the need to protect life is the first responsibility of any government and therefore it trumps the other rights," he said.
"We have 3,000 unsolved murders connected to the Troubles in Northern Ireland and I think it would be very difficult for the Historical Investigations Unit to pursue investigations into those murders if it didn't have access to this bank of fingerprint and DNA evidence."
The Historical Investigations Unit has not begun work as the Stormont House Agreement has yet to be implemented due to the impasse over welfare reform.