A final police search for a man wanted in connection with the death of his mother has been completed.

On Wednesday, approximately 20 police search and rescue staff, alongside volunteers, looked for Jeremy Robertson in the areas of a carpark at Rotorua's Blue and Green Lakes lookout where a car he was using was earlier found.

Robertson was the only person of interest in the death of his mother, Karen Gilbert-Palmer, who was found dead in Pahiatua on October 15 last year.

Detective Sergeant Richard How said since Robertson's car arrived at the carpark there had been no activity on his bank accounts or phone.

Robertson had been driving a red Mitsubishi ASX, registration QGU91. (File photo)

Supplied/ NZ Police

"Given these facts, police believe the most likely scenario is that he died shortly after arriving in the Green and Blue Lakes area," he said.

Robertson and any of his suspected belongings have not been found.

"Police remain committed to locating Jeremy if at all possible, to provide the closure that Karen's loved ones deserve," How said.

Further smaller scale searches would carry on in the future.

How said police still wanted to hear from anyone who could help with their investigation.

That included anyone who had previously found any medication packets or red or blue clothing in the area surrounding the Lakes and nearby tracks.

Mother's concerns

RNZ earlier revealed Robertson, who was believed to have had a history with mental health services, was planning to leave the home on the day his mum died and take a bus to Rotorua.

Gilbert-Palmer's niece, Barbara Evans, said her Aunite, who she called Narnie, would regularly message her talking about her son and his mental health.

Evans said it appeared Robertson's behaviour was "escalating" in the weeks before Gilbert-Palmer's death.

Evans shared a series of messages she exchanged with Gilbert-Palmer.

On 8 October, a week before she died, Gilbert-Palmer messaged Evans and said "I tell u wat, he was better when he was on the drugs and vape, more chilled out. More aggressive now. [sic]"

She said her son was "dead against drugs now".

The following day, Gilbert-Palmer said her son "has been nice for one day, now back to wat [sic] he was".

In another message she wrote Robertson "can be so nasty at times".

Gilbert-Palmer said she wished her niece didn't live so far away so she could go and spend a few days with her.

Later that evening she messaged that he had "settled down".

Then, on October 12, Gilbert-Palmer told Evans her son was going to Rotorua by bus on October 15.

"He decided on hus [sic] own, to much stuff going on down here, having a go at people verbally."

Gibert-Palmer said she would "fill in" her niece once Robertson was gone. It was the last time Evans heard from her.

Evans said she was "absolutely devastated" when she heard her Auntie was dead.

Anyone with information could contact police on 105 using the reference the file number 251015/6286.

Information could also be provided anonymously via Crime Stoppers on 0800 555 111