A post mortem examination has established that homeless man Tama Retimana was assaulted before he died.

The 29-year-old had been camping with his partner near Pine Beach Reserve, on the eastern side of the Waikato River, and was last seen on Christmas Day before his body was discovered downstream by a kayaker a week ago.

He was found in the river wearing only black boxer shorts and black socks.

Detective Sergeant Terri Wilson said the police focus is now on the occupants of the campground situated at Pine Beach.

Police are trying to retrace Mr Retimana's final movements and said his partner is helping with their inquiries.

They are continuing to speak to members of the homeless community to build a picture on Mr Retimana and his close associates.

.