The second explosion ended all hope of a rescue attempt.
If there were any survivors from the first blast, all hope of saving them ended then and police called off the rescue.
A clunk sound in a video showing the second explosion led to speculation the mine's conveyor belt may have been turned on, creating a spark.
But police today announced it had concluded its investigation into and found no evidence to suggest that the conveyor belt was operated or started at any time after the first explosion on 19 November 2010, and no evidence of any causative link to the three subsequent explosions that occurred between 24 and 28 November 2010.
It found no evidence that anyone gained access to a CCTV-monitored hut near the mine portal where the conveyor belt was operated from.
Nor did it find that anyone with the required technical knowledge had accessed computer systems to deactivate audible alarms which would have sounded prior to the belt being started.
The police statement also said that, after consulting with experts, it was concluded there was no evidence that there was an explosive atmosphere of gas adjacent to the conveyor belt system or allied electrical circuits.
Police met with the Pike River families today to inform them of the outcome of the inquiry.
The mining disaster claimed the lives of 29 men.
A planned re-entry of the mine this week was put on hold due to elevated oxygen levels at the far end of the drift.
