But senior fire risk management officer Robert Watson, who investigated the blaze, yesterday quashed those suspicions.
"There's no reason to support any of the small-town community gossip and rumours. The Fire Service has concluded it's investigation ... I can tell you that it's not suspicious."
It was believed that Mr Brady and Mr Walker were "both in bed asleep" when the fire broke out, Mr Watson said.
The survivor had been able to escape the blaze and bang on the window of a neighbouring boat for help, but it had been too late for his friend.
Detective Inspector Scott Beard said the police investigation had also wrapped up.
The future of the other liveaboard boaties in the bay was up in the air, however. Some locals who consider the "vagrant" liveaboard community a blight on the landscape say the death was an accident waiting to happen - and they want the boats gone.
"The situation has got out of hand," former island councillor Jo Holmes recently wrote on her blog.
"When a situation like 'liveaboards' at the Causeway develops and proliferates, it needs attending to.
"Many of the boat dwellers have severe mental health issues. Conditions on board are often a health and safety hazard. They risk damage to themselves and to others housed in the boats around them."
There have been reports among the community of theft and vandalism, drinking and fighting. Some of the liveaboard boaties - who are technically all living illegally under council law - have been asked to move away from the bay.
But others have chosen the boat life for other reasons, cause no trouble, and think they should be allowed to stay.
Steve Matatahi and his wife Mary, for example, both university educated, have raised and homeschooled four children on their catamaran Kukurei in the bay.
"The majority of people down here stick to themselves and get on with their lives. Most people just want to be left alone and get on with things," he said.
"We're not transient people and we're not deep sea farers. I'm going to fight it. We need land so we can go to the shop, go to the doctor's. Everybody here has been here forever."
Local council board chairman Paul Walden said the death "will be a catalyst for change" for the liveaboard boating community.
The problem, however, was the majority of the liveaboard group had nowhere else to go, he said.
"There's no alternative for these people down there. My primary concern is for the welfare of the people ... my reluctance to push them out to sea is there's nowhere else for them to go. Sure it'll tidy the beach, but it won't solve the problem. The alternative is for them to go and sleep under a bridge."
A specific bylaw for the island would be pushed in the council Unitary Plan, Walden said, allowing some boats to stay - but with tighter restrictions.