Detective Senior Sergeant Mike Sears acknowledged the murder was as much a wheredunnit as a whodunnit.
Adding to the mysteries of the case is that Mr Stevens' body was found near the car after dawn by a member of the public six hours after police attended what was then thought to be an abandoned car.
Mr Sears said an autopsy indicated Mr Stevens had been beaten, and died of stab wounds to the torso.
Mr Stevens was last seen alive about 10.30pm, leaving a Lower Hutt supermarket with a six-pack of beer.
The armed offenders squad raided the Oxford Tce address early last Saturday, 18 hours after Mr Stevens' body was found. At least three adults were in the house at the time.
The tenant of the Housing New Zealand property is a woman aged about 30 with young children.
Police are uncertain whether the males lived there or were visitors.
Mr Sears said the occupants had been spoken to but the exact relationship Mr Stevens had with them had not been determined.
He was known to others at the house besides the woman. No arrests have been made.
A neighbour told the Herald the woman moved in about two months ago. She had not heard anything untoward the night Mr Stevens died.
The occupants have moved out and forensic scientists have spent the week at the cordoned-off house searching for clues. Items removed include towels and two cars.
Police have yet to get results from forensics. "We can't say that it's a crime scene. Examinations are still to determine whether or not it is," Mr Sears said.
On Wednesday night - six days after Mr Stevens went missing - Paekakariki Hill Rd was closed while forensic examinations were done in the area where his car and body were found.
Police were yet to work out what occurred there: a homicide, or whether Mr Stevens was murdered elsewhere and disposed of in the bush overlooking Kapiti Island.
"This wasn't a motor vehicle accident," police said.
There was no indication of robbery. The only personal item yet to be found is one of Mr Stevens' brown leather shoes.
Police are working to build a picture of Mr Stevens and associates. This includes "Facebook chatter", including comments threatening retribution.
One posting said: "You didn't have to take his life but I pray someone takes yours baldhead."
"At this stage, by all accounts he was highly regarded and loved by family, friends and associates," Mr Sears said.
At the funeral on Thursday, Mr Stevens' uncle and godfather, David Hindmarsh, described him as artistic and "a meaning-of-life junkie searching for answers" who loved his mother Christine's cooking so much he never thought of leaving home.
He had worked as a painter and landscaper and was about to become a truck driver, had done community-development charity work in the Philippines and was prone to offering random acts of kindness.
A drummer during his days at Wellington High School, he played with musicians who went on to find success in the band The Phoenix Foundation, and more recently explored his artistic side by studying drama and gaining bit parts in Sir Peter Jackson's films King Kong, Avatar and Lord of the Rings.
Mr Hindmarsh said family and friends were left with overwhelming grief and unanswered questions.
Family home, Johnstone Grove, Taita
Photo / Mark Mitchell
Matthew Stevens left here about 10pm on Thursday, November 27, with the intention of visiting 78 Oxford Tce in Epuni, a few kilometres away.
78 Oxford Tce, Epuni
Photo / Mark Mitchell
Being treated as though it is a crime scene. It has been taped off for a week and forensic scientists have been working at the property each day. It was raided by the armed offenders squad less than 24 hours after Mr Stevens' body was found.
However, police say they are yet to establish whether Mr Stevens actually arrived here, or his relationship with people linked to the address.
The tenant is a woman aged about 30 who has children. A woman and "a number of men" were at the house when it was raided
