A former top police officer has backed a new theory that a conveyor belt was switched on at Pike River Mine.
John Canning was an officer for 40 years on the West Coast, and was working at the mine after it exploded. Now he's breaking ranks to speak up about what he thinks went on at Pike River.
He's thrown his support behind a new theory about what caused the second explosion five days later that ended all hope for the 29 men inside.
The theory, put forward by family member Dean Dunbar, relates to the mine's conveyor belt and whether someone turned it on, creating a spark which ignited the methane in the mine.
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Mr Canning says he wasn't working the day of the second explosion, but remembers during the lead-up to it that mine management wanted to turn the belt on.
"They expressed their thoughts and they wanted it, tried, but we resisted while the risk was high."
Documents show some of the reasons for starting the belt were to check if the mine was obstructed or to give survivors a chance to ride it out.
"[There's] quite a strong documentary trail as to the thinking and making of that decision," says Mr Canning of the documents.
Newshub asked Police for documentation that showed a final decision around the belt, but they say they can't find one.
They say the belt theory is just a theory, but they can't rule it out. They invite anyone with any information that could assist the investigation to contact Police directly.
Police say that on their current knowledge, there is no information the belt was switched on. Mine experts say the belt movement seen in footage was caused by the second explosion.
Current and former police staff say risk assessment was not approved and it was not switched on, but police are investigating to answer questions for the families of the victims.
Right up until August last year, Mr Canning didn't believe the conveyor belt was switched on, which he told both police and families spokesman Bernie Monk.
But he changed his mind when he was told otherwise by police colleagues he won't name.
"It is compelling, the documentary evidence - and coupled with the corroboration of the video," he says. "It is compelling."
He says the new investigation into whether the conveyor belt sparked the second blast is needed.