Police still do not know when Ross Bremner killed an elderly couple at their remote property on the Kawhia Harbour.
But they say his car was seen there before he killed his mother, Clare, at their Otorohanga home earlier this month.
Bremner's body was found alongside those of Mona Tuwhangai and Maurice O'Donnell at their property in Kinohaku three days after he attacked his parents on 4 October, leaving his mother dead and his father, Keith, critically injured.
Police said they were still trying to work why Bremner was at the Kinohaku property and how he got there.
They had not been able to confirm any link between the elderly couple and the Bremner family.
They were continuing to interview people and the results of forensic tests were expected in the next couple of weeks.
The police said they were hopeful this would paint a clearer picture of what happened.