There was a sighting of Ross Bremner's car at his victims' home before he went on his murderous rampage, say police.

Waikato Police Detective Senior Sergeant Ross Patterson today said officers were continuing their investigation into the deaths of Clare Bremner, Mona Tuwhangai and Maurice O'Donnell three weeks ago.

Ross Bremner is believed to have killed his mother, Clare, and critically injured his father, Keith, with a knife at their Otorohanga home before fleeing to Kinohaku, near Kawhia.

It was there that his body was found four days later alongside elderly couple Mona Tuwhangai and Maurice O'Donnell.

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Until today, it was believed that Bremner did not know his elderly victims before the attack.

However, it is now a possibility that he visited the couple before his attack on his parents.

"Police have also received accounts that the vehicle used by Ross Bremner was seen at the Kinohaku address earlier that day," said Patterson.

He said that police believe Clare Bremner was still alive at 4.19pm on Tuesday, October 4 and died sometime before police were called to the family's Cruden Ave address in Otorohanga at 8.30pm.

It has not yet been established what time the couple at Kinohaku died, but their bodies were found on Friday night when a friend went to check on them.

"Police are still trying to establish why Ross Bremner was at the Kinohaku address and how he got there, but based on enquiries to date have been unable to confirm any connection between this address and the Bremner family's," said Patterson.

"Police are continuing to interview people and further forensic results are expected in the next two weeks, which investigators hope will paint a clearer picture of what occurred.

"The case remains under investigation and will be subject to a Coronial inquest."

Keith Bremner's condition was improving, but he was still an inpatient at Waikato hospital after suffering life-threatening injuries in the attack by his son.

Information can be reported to the Operation Arctic team on 07 858 6200, or to the anonymous Crimestoppers hot line on 0800 555 111.