The police sergeant accused of assaulting five prisoners faces an Independent Police Complaints Authority investigation and an internal police inquiry which could take months.

An Auckland District Court jury found Sergeant Martin James Folan not guilty of six assault charges yesterday after deliberating for six hours.

The court heard from a total of 27 witnesses, at least five of whom said they saw Mr Folan assault prisoners. Three other police officers gave evidence for the defence and said they had never seen him use excessive force.

But the police officer with 14 years' experience will now face an internal disciplinary hearing.

Superintendent Bill Searle, commander of the Waitemata Police District, said an employment investigation would begin straight away.

Mr Folan's lawyer, Richard Earwaker, said outside court that the process could take six months. Meanwhile his client's work life was still on hold.

"As you can appreciate, since he was stood down on February 10 last year there has been a tremendous strain on him. It has been incredibly stressful. "

Mr Earwaker said his client had not been able to comment in the media and was still unable to with an IPCA and employment inquiry ongoing.

At the trial, the Crown alleged Mr Folan had acted in anger when he elbowed a teenager in the face, banged a man's head on a police station's concrete floor, kicked a man in the groin or stomach, throttled another man, and kneed a fifth man in the groin.

Mr Earwaker told the court the elbow and the head banging never happened or were an accident. He also reminded the jurors that police officers could use reasonable force against violent, intoxicated prisoners.

Outside court, Mr Earwaker said his client would like to keep his job with the police. He said he understood the police had to investigate their own personnel when complaints were made but the process was "incredibly difficult" for those involved.

"We don't want to get a situation where police officers are afraid to do their job because of who is looking over their shoulder."

He said officers had the authority to use reasonable force against violent people and some situations could not be "finely judged".

Mr Folan had tears in his eyes as he left court. He said he was thankful for the support of his friends and family.

One of Mr Folan's alleged victims, Joseph McGee, said the verdicts were "heartbreaking".

He said it was emotional taking the witness box to give evidence.

"I've never done anything like that before. I almost wanted to cry ... at one stage I was getting frustrated."

He said he had been having a few drinks with his flatmate when he was beaten up outside a bar.

His flatmate called an ambulance but when police turned up, Mr McGee was arrested for disorderly behaviour.

Mr Folan later allegedly kneed him in the groin. Mr McGee had to have his testicle surgically removed.

But the charge against Mr Folan of injuring with intent to injure Mr McGee was dropped during the trial.