Butler's partner, Dana Corbett, said it had been an extremely difficult five months for her and Butler's family as they struggled to cope with how he died.
She said as every day passed, they hoped someone would be held accountable.
"It's good the police are being thorough but we just want closure and justice for my darling Nev."
Detective Senior Sergeant Mark Van Kempen told the Rotorua Daily Post he could understand the family was anxious, but there were "intricacies" with the case which meant it would take time.
He said police were unable to arrest anyone until they had all the evidence, which they were still gathering.
However, he confirmed the case was still very much an ongoing inquiry and he was confident there would be an update.
Butler was released from prison five days before he died. Corbett and his family said he was looking forward to turning his life around and was on track to making a fresh start, including getting into physical fitness.
On the night of his death, he had been enjoying the company of his mother, Julie Donner, who lives around the corner from Steeles Lane, when he got a phone call to go to the flat and return a mobile phone.
Neville Butler (right) with his 'Ma' Julie Donner. Photo/supplied
At 5am the next day, police knocked on the door of his mother's house and she was informed her son was dead.
Donner has previously told the Rotorua Daily Post the family were desperate for answers.
"We hope we get to the bottom of what happened so we can have closure," she said in October.
