Winston Peters says the Pike River 29 were "murdered by neglect", putting re-entry into the mine firmly on the agenda for next year's election.
The New Zealand First leader pledged to be one of the first back into the mine after a new report from a UK expert, which lays out a safer method for re-entry, was released on Tuesday.
His promise, made at a rally by Pike River families outside Parliament, has been criticised by new Prime Minister Bill English as "trivialising" the situation.
"Look I don't think anyone will take that seriously, there's a serious safety issue there and he shouldn't trivialise it," Mr English said on Tuesday.
But Mr Peters came out strongly in response, telling Paul Henry on Wednesday he had experience in the industry.
"With the greatest respect, I used to work 11 miles underground back in the 70s in Australia, I've got some small idea of how dangerous this is," he said.
"That complex lost a man a mile, so I'm not just going off the top of my head, I do understand the safety issues."
Mr Peters believes the attempt to seal up the mine with 30m of concrete ("that's like the Maginot Line") is part of a larger cover-up by the system.
"This is how extreme these people are - trying to shut down ever finding out in the period they can be held, while they're alive, culpable for actually seeing people murdered by neglect," he said.
"Twenty-nine people died there, all these families and the whole industry is waiting for answers."
Mr Peters believes the mine could well be a crime scene.
"I think the level of cover-up going on, and the level of recalcitrance against what they promised suggests they don't want to find out if they're seriously culpable on a criminal level as well."
Mr Peters is making no apologies for taking a strong stand on the Pike River re-entry, which has become Mr English's first major issue to deal with as Prime Minister.
"Those people down there are the heart and soul of the West Coast... and they've been treated like they're rubbish - that's the fact of it. Yes it's a bottom line and [Mr English] should get that through his head right now."
Mr English had previously ruled out meeting with families spokesman Bernie Monk on Tuesday - his first full day as Prime Minister - saying he "wouldn't have time".
However, the pair did bump into each other in the Parliament precinct and Mr English said he would consider meeting with the families publicly.
The UK report suggests ownership of the mine should be handed over from Solid Energy to a special entity, but Mr English didn't think that would change anything.
"Whoever owns the mine, it doesn't make any difference to whether it's safe or not and whoever does own it still has to make decisions about safety."
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