The PSNI has apologised unreservedly for taking more than 20 years to investigate properly the IRA abduction and killing of Jean McConville in 1972. "It should have been investigated better," Chief Constable Sir Hugh Orde said.
However he admitted he was not hopeful of securing convictions so many years after the crime. Efforts to uncover the truth about the killing would continue and close co-operation with the Garda would continue, he added.
Deputy Chief Constable Paul Leighton said it was appropriate that police acknowledge any shortcomings.
"If there is a failure in police action, then we need to say sorry and that is what I am doing," he said.
The PSNI was studying the report by Police Ombudsman Nuala O'Loan, which says that a proper police investigation was not carried out for more than 20 years.
Mr Leighton, a member of the former RUC before it became the PSNI in 2001, said it was also important to recognise the security situation at the time of the McConville murder.
"In 1972, there were 10,631 shooting incidents recorded, 1,853 devices used, 470 people were killed including 17 police and 131 soldiers, and almost 5,000 people injured. Policing operated in an entirely different environment than it does today," he said.
However, he also said he was not using these statistics as an excuse for any police failings.
Mrs McConville's son Michael said he blamed the RUC as much as the IRA.
"They didn't do enough work on the case in the first place, I think it was a big let-down for the McConville family," he said.
"If police had reacted more quickly, my mother might have still been alive today. I think that to start an investigation 20 years later is a bit late."
Chief Constable Sir Hugh Orde rejected this: "The RUC did not murder Jean McConville. She was murdered, and we are very clear on this, she was murdered brutally by the Provisional IRA."
Mrs McConville's daughter, Helen McKendry, said the police admission of failure had "come too late".
She said that had the police acted quickly on information given following the abduction her mother might not have been murdered.
"They could have arrested people who were involved, the names were given. Maybe one of them would have said where she was taken and they could have put a search out for her and found her alive."
Mrs McKendry said she was not hopeful that the full truth surrounding her mother's disappearance and murder would emerge.
This is despite the referral of the case to the PSNI's historical inquiries team, which is trying to solve nearly 2,000 crimes.
Alex Attwood of the SDLP said the report was "a deep indictment of the RUC".