A cyclist who saw a teenager die in a canal thought he must been a violent person because the police were not going in to save him.
When Ailish Tynan arrived at the canal at Walthamstow Marshes in east London in July 2015, another onlooker told her "the police have chased that fella into the water", she told St Pancras Coroner's Court.
Ms Tynan did not see Jack Susianta, 17, of Hackney, east London, go into the canal but saw him "treading water like he was trying to stay in one spot" as police looked on from the grassy bank.
Ms Tynan told the inquest into Jack's death: "There did not seem to be any sense of urgency, which made me think 'Gosh, maybe he has got a knife' and 'Why is nobody doing anything?'"
The Metropolitan Police have denied claims that they refused to go in to save the teenager.
Ms Tynan told the court: "We made the assumption ... The first thing I said to the guy was 'Why is nobody going in?' and he said 'I do not know - it is only 5ft deep'.
"Everyone seemed very hesitant. I thought 'Gosh, this might be some kind of dangerous individual' because they had no-one going after him."
Ms Tynan, an opera singer, described it as an "emotional" episode and said she was not an expert on life-saving but added: "I assumed he was dangerous because no-one was going in to get him. There were about 10 policemen there."
She saw police throw a rescue line "about 20 times" to Jack.
A woman officer was shouting "Grab it, grab it" and it got to within about 5ft (1.5m) of him, she said.
Ms Tynan, who had been on a bike ride with her musician husband, said: "I was saying I cannot swim at all. My husband is not a great swimmer. There was an Italian guy who said 'I am a good swimmer'.
"No-one did anything because we thought the police would do it."
Ms Tynan felt "relief" when she spotted a single sculler on the water and thought "there is a hero coming".
The sculler started looking for Jack but she thought he could not find him.
With just one more stroke, the sculler could have brought his boat within reach of Jack but the teenager went under and did not come back up, she said.
Ms Tynan added: "I could not really say if he (Jack) got too tired, tried to get away or pushed himself under - except that it was so close. If he had waited two more seconds, he could have got it."
During all this, Jack, who was a strong swimmer, never said a word.
Ms Tynan said "he seemed to be biding his time" and a policeman waded into the water.
Her husband, Keith McNicoll, said the officer was making very careful steps in the water, giving him the impression that he "was not entirely comfortable".
He accepted he could not see if the officer was sweeping the canal bed with his feet for obstacles.
He also said he never heard the police tell anyone not to go in.
He described it as "surreal".
Jack was not splashing about and there was a "feeling of serenity" apart from the policewoman who was shouting for a rope.
He felt that if any officer was in charge then it must have been her.
In contrast sculler Sean O'Shea praised the police and described the officer who waded into the water as "brave".
Mr O'Shea, who estimates he has rowed over 30,000 miles on that water over 20 years, described the river as "very dangerous".
It has shopping trolleys and motorcycles along it plus it is at least 8.5ft deep in places.
"You cannot tell how deep the river is," he told the court.
Mr O'Shea said he could not save Jack as he had an injured shoulder and feared the teenager might grab and topple his unstable boat. This would have meant they both could drown.
In defending the officers, he said: "They were frantically trying to get him to get hold of the (rescue) ring. He instinctively seemed to be moving away from it."
Those witnesses who thought the dramatic scene was quiet were probably in a more distant position because the buzz of the overhead helicopter made communication "almost impossible", he noted.
Mr O'Shea recalled: "The helicopter was incredibly loud. My feeling was that if they were in radio contact, they should have warned (it) off."
He said the police pleaded with him to assist and an officer said "please help him".
"It was with a note of pleading and desperation in his voice - it was not just an instruction," he added.
Mr O'Shea, who at this point still thought that the man in the water was a criminal trying to escape from the police, rowed back to see if he could reach Jack. In a harrowing scene, he saw him go down for the last time.
Mr O'Shea said: "He went under. I could see him about 50cm out of my reach. I could see him I think from the top of his head which was slightly back and across his forehead. I could see a few bubbles as he sank."
Mr O'Shea described Jack as uncoordinated and thinks he had taken on water from the first time he went under.