Police have denied it "deliberately withheld" video showing a robot going into the Pike River mine, filmed just three months after the final explosion.
In the video, two men wearing mines rescue uniforms can be seen working on the robot, which later can be seen smoking or steaming - but not catching fire.
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Twenty-nine miners died in the disaster and the Government has argued gas levels make it too dangerous to re-enter the mine to retrieve the bodies.
Family members of those killed allege the video has been kept from them until now, which Deputy Commissioner of National Operations, Mike Clement, denied on Monday.
"Video footage from this robot operation on 15 March was handed to police and excerpts were shown to the families at two family meetings on 23 and 24 July 2011 in Greymouth and Christchurch," he said in a statement, adding, "About 30 family and supporters were at each meeting."
"Police and other parties have shown a large amount of video footage to the families since 2011."
Police originally told Newshub the mine was in police control at the time of the video and the video wasn't passed onto either the families or the Royal Commission because "it was assessed as having no evidential value".
Dep Cmsr Clement has now clarified the mine was in the hands of the receivers, and said the statement was based on a "misunderstanding", thinking the footage in question was from a different robot which was sent into the mine on November 24 2010.
"We have been open about this footage and have not sought to withhold anything which we believe would be relevant and of interest to the families," he said.
Prime Minister Bill English admitted to The AM Show on Monday he didn't know the footage even existed.
"I first saw it late last night," he told host Duncan Garner.
But on Monday afternoon, speaking at the post-Cabinet news conference, Mr English reiterated that police had shared the video with the families - and that it had been supplied to the Royal Comission.
"The showing was to ensure that the families were not caught off-guard when the information was provided to the enquiry," he said.
"All of the video footage was available to the Royal Commission."
He said the men seen in the video were in a container installed at the entry into the mine, going "no further than 2m into the mine during that operation".
"At the time the drift was inert because it had been pumped full of nitrogen," Mr English said.
"The fact remains the video does not change the assessment that the mine is unsafe for manned re-entry."
On Sunday, a spokesperson for Nick Smith, Acting Minister of Conservation for Pike River Issues, said he hadn't seen the video either.
"No one from the Government has viewed this footage, though the Government has been advised it was used by Solid Energy as part of its extensive investigation into whether the mine was safe to enter," they said.
Dean Dunbar's son Joseph was 17 years old when he was killed in the Pike River disaster, just a day after his birthday.
Mr Dunbar first saw the video on Sunday, when shown by Newshub.
"We are going to peel back the litany of lies and expose this for what it is," he said.
"How could they do this to Joseph and the other guys? Why? They've had the footage - we haven't."
Anna Osborne's husband was killed in the disaster and told The AM Show the families have filed a request under the Official Information Act for access to the full 30 hours of police footage.
She also said the video hadn't been shown to the families, saying it "reeks" of a cover-up.
"What the footage shows is what the families have tried to convince the Government for a very long time - that the drift and its construction is not compromised at all by the explosions that have gone through," she said.
"We have been waiting six and a half years, and we've had no justice."
Dep Cmsr Clement confirmed the OIA request had been made, saying police have been "absolutely committed to ensuring transparency with the families".
"We are working to expedite the release of this footage and other material as soon as we can, however there are more than 30 hours of footage and photos from various sources in different data formats that needs to be collated," he said.
Work is underway for an unmanned exploration into the mine, Mr English said.