A cop who left a loaded Glock pistol in one of Parliament's public bathrooms will not be charged and will keep his job, 1 NEWS can reveal.
The Diplomatic Protection Squad officer - assigned to protect the Prime Minister and other VIPs - was instead disciplined, alongside a fellow officer.
Now police have closed the investigation, more details of the June 2016 incident have come to light.
The DPS officer put down the weapon when he visited the bathroom on June 16 but got all the way to Wellington airport before he realised he had forgotten it.
He asked another officer travelling with him to return to Parliament to recover the firearm.
But the second officer was too late - just moments before he got to the ground floor toilets, the gun was discovered by a member of the public.
It had been there for almost an hour and a half.
A spokesman for Police told 1 NEWS both officers were investigated and will continue to work with the DPS.
"In relation to the officer who left the firearm, the investigation accepts there was no intention to leave the firearm in the bathroom, and the investigation explored the options available to recover the firearm at the time," he said.
"This matter has been dealt with by way of an employment process with the individual and the second police officer, the details of which remain confidential between them and Police."
Assistant Commissioner Mike Rusbatch said it was a "serious incident" but was "thoroughly" investigated.
"We are in no doubt about the potential risk which arose from this incident.
"Our staff are human and we accept that the firearm being left in the bathroom was a genuine mistake.
"However, the loss should have been dealt with differently once it was discovered to minimise the risk to the public.
"This incident was without precedent and I am confident that lessons have been learned regarding application of our operational risk assessment model, and our expectations of staff."