PC David Ennis said he believed Leon Patterson, 31, had been trying to evade being interviewed over a shop robbery for which he had been arrested.
Patterson, a heroin addict, was found dead at Denton police station, Greater Manchester, four years ago.
A jury at an earlier inquest said that Patterson, of north London, had been unlawfully killed and that he should have been transferred to a prison hospital. It had heard the cause of death was "unascertainable".
But the police overturned the verdict in the High Court, which ordered a new hearing. Patterson's family allege he was beaten by officers. The inquest is expected to last two weeks.Reuse content