The multiple incident scenes kept police forensics teams busy for most of yesterday as they examined three addresses across East Auckland.
As well as the stabbing site and the crash scene, Armstrong's house in Kells Place was also cordoned off and under guard.
Police said after the fatal stabbing, Armstrong went to his home in Kells Place, where he lived with his parents.
He got back into his car before crashing on Gosford Drive.
Detective Inspector Jim Gallagher said police were not looking for anyone else in relation to the death.
Mike Slade said as he watched television at his home he heard an "almighty bang" as the car crashed into his house about 11.30pm on Friday.
"It shook like an earthquake," he told 3News.
Firefighters had to cut Armstrong from the car.
Police were last night trying to contact the dead man's family. He was described by neighbours as a young Asian man. He had lived at the address for a few months.
It is understood the dead man's family divided their time between New Zealand and overseas.
A neighbour described the Armstrongs as a "good family" who attended the C3 church in Howick.
Gallagher asked anyone who saw a two-door, 1996 silver Mitsubishi Mirage sports car between 9.30pm and 11pm on Friday, between Howick and Half Moon Bay, to call police.
People can call Counties Manukau Police on (09) 261 1300 or Crime Stoppers on 0800 555 111.
