How a man ended up face down in the River Stour less than an hour after he was released from police custody will forever remain a mystery.

Police have told of a lost 21 minutes in the tragic life of former teaching assistant Carl Lesniewicz, who drowned in Canterbury last year.

His ex-partner Jacqueline Hall told an inquest that she and Mr Lesniewicz, 38, had split up seven months earlier because he had not been able to overcome his addiction to drink.

The hearing in Margate was told that Mr Lesniewicz was arrested on September 8, 2014, at a house in Herne Bay, where he had been staying with a fellow alcoholic.

He spent the night in a police cell and was released at 2.45pm the next day.

At about 3.30pm on September 9 he was found floating face down in the section of the Stour which runs parallel with North Lane and towards the footbridge into the Causeway car park.

Acting Det Sgt Brad Shingles said at 3.33pm a 999 call was made by people walking along the alleyway next to the river.

"I would love to tell you what happened in those missing 21 minutes, but I can’t..." - Acting Det Sgt Brad Shingles

The officer said Mr Lesniewicz was last seen on a CCTV camera at the foot of St Peter’s Street at just after 3.10pm.

“There’s a space of 21 minutes between Carl being seen on CCTV and the 999 call,” Det Sgt Shingles said.

“It’s not known what then happened to Carl or how he came to be in the river. I would love to tell you what happened in those missing 21 minutes, but I can’t.”

The detective, however, rejected the theory that someone else may have been involved in Mr Lesniewicz’s death.

He went on: “There’s no witness evidence, there’s no CCTV evidence and there’s no forensic evidence of third party involvement.

“There’s no suggestion of an attack. This was either an accident or suicide, but there’s nothing to prove the latter.

“From the police’s point of view, his death is unexplained.”

Det Sgt Shingles said police had arrested Mr Lesniewicz at a flat in Herne Bay High Street occupied by alcoholic Dean Attwood on September 8.

Mr Lesniewicz had failed to attend a court hearing for shoplifting and was picked up on a warrant issued by magistrates.

On September 9 he appeared at court via video link from the police station and received a conditional discharge plus court costs.

Sgt Simon Coughlan, who oversees the cells at Canterbury police station, said Mr Lesniewicz had been co-operative and in good spirits.

“He was fairly upbeat and there were no threats of self-harm,” Sgt Coughlan said. “Neither was there any evidence of alcohol withdrawal.”

A mandatory investigation by the Independent Police Complaints Commission concluded that Mr Lesniewicz’s arrest and detention are unconnected to his death.

He left the police station at 2.45pm and Canterbury’s CCTV cameras captured his journey as far as the Westgate Towers.

At 3.30pm John Bower was walking along the river when he came across a man and a woman who had found Mr Lesniewicz floating face down in the water.

Mr Bower got into the river and together with another man they pulled Mr Lesniewicz out just before the police and ambulance arrived.

A post-mortem examination later found that he died from drowning. He had small bruises and grazes on his body, but pathologist Peter Jerreat said these were likely to have been caused by lifting him out of the water and by later efforts to revive him.

Marks on his head appeared to be from injuries sustained in March, while toxicology tests detected no traces of alcohol in his system.

Coroner Ian Goldup recorded an open verdict.