Thomas Orchard, 32, had been arrested on suspicion of a public order offence and taken to the police station.
He suffered a cardiac arrest whilst being held in custody at Exeter's main police station in October 2012.
The court heard that Mr Orchard, the caretaker at St Thomas Church in Exeter, was held down and a large webbing belt was put across his face.
He was then freed from restraints - making "little or no movement" - and then left lying face down in the locked cell for 12 minutes before officers re-entered the room to find that he was not breathing.
Mr Orchard, who was diagnosed with paranoid schizophrenia, died in hospital seven days later.
Custody Sergeant Jan Kingshott, 45, civilian detention officers Simon Tansley, 39, and Michael Marsden, 56, face one joint charge of manslaughter, alleging that they unlawfully killed Mr Orchard by gross negligence.
Prosecutor Mark Heywood QC told the jury at Bristol Crown Court that the combination of force and physical restraints, coupled with a "complete failure" to realise Mr Orchard's mental health condition led to him being starved of oxygen.
"That situation continued for over five minutes, deep within a police station, whilst he was restrained at hand and foot," Mr Heywood said.
"At the same time, no-one of those directly responsible took sufficient care to see that he was breathing properly - or at all.
"Instead, he was left in a locked cell, under remote observation for a further 12 minutes until his true condition was discovered. By then, it was too late. Much too late."
The jury, of six men and six women, has been told that the case is a retrial.