Pike River families spokesperson Sonya Rockhouse says there's been a cover-up and has called for a "proper investigation" to uncover more evidence.
Her comments come after the discovery a potentially vital piece of evidence from the 2010 mine disaster has gone missing.
An electrical cabinet that was blown to the mine surface has not been seen since it was taken by a helicopter leased by the company.
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Former mines inspector Tony Forster, who is now advising the families of those killed in the tragedy, said after it was photographed it was flown to the Pike River Mine office.
Mr Forster told The AM Show he provided a photograph and a formal statement to police on Monday last week.
He said a lot of electrical equipment used in the mine was unapproved and uncertified.
Ms Rockhouse, whose son Ben died in the explosion, said the families were "absolutely shocked" to see the photograph.
"There will be more [missing evidence], and there are people who know exactly what's out there," she told The AM Show.
"It's time for those people to come forward and tell us the truth."
Police have confirmed they are reinvestigating.
Ms Rockhouse says families want "truth, justice and accountability".
She believes the re-entry will take place mid- to the end of March.
Police plan to complete a full forensic examination once the drift is fully recovered.