Officers failed to properly monitor a man who attempted suicide while in custody, the Independent Police Conduct Authority says.
The man was picked up by officers in October 2016, after police received calls fom his partner who said he was suicidial.
The Authority has found officers at the Wellington District Custody Unit did not correctly evaluate the man's condition, which meant that he was not constantly monitored.
"Mr X was inappropriately evaluated as 'In need of care and frequent monitoring'," the report read.
The man was put in a cell at 3am, and only checked once before his suicide attempt at 4.30am.
"Officer E should have recognised that he needed to be evaluated as 'In need of care and constant monitoring' until the Crisis Resolution Service staff were able to assess him," the report stated.
The Authority said officers should have discussed taking the man straight to hospital, where he would have access to a higher level of mental health care.
In a written response, Wellington District Commander Sam Hoyle admitted other options to district custody should have been considered.
"Mental health incidents are complex and our staff have to make quick decisions when responding to them," he said.
"We expect high standards of care from our staff during such events and following this incident these standards and expectations have been reinforced."