"On this occasion, we fell below the standards of service rightly expected of us and we have put steps in place to help ensure it does not happen again.''
The investigation found ways in which procedures could be improved and had led to more robust measures being put in place, she said.
The man, 59, had been placed in a holding cell at the Masterton District Court on a Saturday in mid-January.
He had been awaiting a sentence on a drink-driving charge and was on bail.
He appeared in the court that morning and was later taken into the court holding cells after being granted bail. He was in the cell waiting while the bail document was being written up.
Instead of being released, however, he wasforgotten by police staff.
It would be about 48 hours - on Monday morning - when he would be discovered.
As part of the investigation, the Independent Police Conduct Authority had also been heavily involved.
Police said the Authority would continue to monitor the progress being made following the incident.
The man involved is also said to hold no ill feeling towards staff involved, police said, and he and his family were happy about the outcome of the investigation.
Police would not comment when the Herald asked whether the man involved had received any compensation or if the staff member or members involved were disciplined after the incident.
The incident had provided a lesson for all staff, Howard said.
"The lessons learnt from this incident have been communicated with all staff across the area and we are doing all that we can to ensure this does not happen again.''