Police investigating a suspicious death believe they know how the man died, but lack enough evidence for an arrest after being stonewalled by witnesses.

Damien Loder Allen, 33, last month died from head injuries which were not accidental.

Police believe the house where his body was found on September 24 in the Auckland suburb of Hillsborough had been cleaned and his body had been moved.

Several possible witnesses were refusing to co-operate.

Mr Allen had head injuries and police were still waiting on toxicology results.

Detective Inspector Scott Beard told NZPA he believed witnesses may be protecting someone involved in the death.

He would not say how Mr Allen got his injuries, or if they had found a weapon.

Others in Mr Allen's house made 111 calls the night he died.

Four people were in the house when police arrived and others had visited the house on the night.

It was not a party but people were socialising and drinking.

"From the reconstruction and from some of the people we have spoken to we think we know what happened," Mr Beard said.

He said information was still flowing in but police still wanted to hear from anyone who knew what may have happened or knew the people at the house.

Anyone with information should call the confidential Crimestoppers line on 0800 555 111.

- NZPA