Police are remaining tight-lipped about an inquiry into the future of two policemen sentenced today for punching a drunk teenager they had arrested at a party last year.

Gareth John Needham, 38, and Alan Michael Douglas, 32, were both found guilty of assault by a jury in the Auckland District Court in December and last year.

In court today, Douglas was fined $600 while Needham was convicted, and discharged.

The pair have been stood down on full pay since the incident and now face a police internal code of conduct investigation to see whether they can keep their jobs.

"It goes through an employment process so we don't comment on that because it is confidential between the employer and the employee," police spokesman Jon Neilson told NZPA.

He did not know how long the process would take.

The court was told the two west Auckland constables assaulted Joshua Hart, then 18, who had been drinking with up to 50 people at a West Auckland park.

Mr Hart was abusive to police after his drink was knocked out of his hands by Needham, who then struck him twice as he forced him to to the ground and handcuffed him.

The prosecution said that Douglas was struck Mr Hart twice in the face while he was handcuffed.

Needham and Douglas applied for a discharge without conviction after a restorative justice hearing with Mr Hart, who did not oppose the discharge without conviction.

However, Judge Allison Sinclair today declined to discharge the pair without conviction.

She found that the consequences of a conviction would not be out of all proportion to the offending.

Douglas' offending was at the lower end of the scale but was a gratuitous use of violence on a handcuffed person, Judge Sinclair said.

Needham was in the news last week when he gave evidence at the Auckland inquest into the death of two year-old Aisling Symes, who fell through a faulty manhole cover and drowned in the stormwater drain in 2009.

Needham was one of the first officers on the scene when the toddler was reported missing.

He found a manhole slightly ajar but did not tell his superiors. Aisling's body was found down the drain seven days later.