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The criminal investigation into the Hillsborough disaster will look back as far as 1975.

At a briefing today Assistant Commissioner Jon Stoddart, who leads Operation Resolve, said the investigation was "in very good shape to get to the bottom of the causes of death and to get to the truth".

He said 500 witness interviews had been held and people had "shed far more light" on the events.

He said investigators were looking at stadium safety in previous matches going back to 1975.

VIDEO: Operation Resolve chief Jon Stoddart on the Hillsborough criminal investigation

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His deputy Assistant Chief Constable Terry Sweeney said investigations would be made into handheld police camera footage from the gymnasium which had an unexplained 10 minute gap.

Concerns with the "integrity" of the tape were raised by Pete Weatherby QC, representing 22 of the victims' families, at a pre-inquest hearing on Monday .

ACC Sweeney said: "The tape itself will be independently assessed by forensic specialists from Mr Weatherby's chambers and also our own."

* Re-read our updates from the final Hillsborough pre-inquest hearing in London

He said as part of inquiries the individuals who produced the tape and people who were in the gymnasium at the time would be interviewed to give a "thorough understanding" of what happened in the missing 10 minutes.