Two key witnesses told an inquest on Wednesday they were disturbed by what they saw during the arrest of Junior Alexander Manon.

The 18-year-old stopped breathing after police brought him to the ground and handcuffed him near York University two years ago.

A pathologist determined Manon died from suffocation — or 'positional asphyixia' — by the way he was held by the two arresting officers.

Julia Brown said she is still haunted by the image of Manon lying on the ground — one police officer on him holding his arm, another slapping him in the face.

Brown testified Manon stopped breathing minutes after his arrest and needed CPR immediately.

"Any ... person that has [taken] first aid should really recognize right away the person's not moving, take action, don't keep slapping him," she said.

Brown is a bus driver who has first aid training, she broke down in tears when she told the jury she wanted to help but was frozen with fear.

She said she thought the police might come after her if she intervened.

Another witness, Rosa Berdejo-Williams, testified she saw an officer smash Manon's face repeatedly with a police radio.

"I was torn by what I saw. It didn't look right," she said,

But she was too afraid to act.

Also on Wednesday the coroner ruled the jury won't be able to see a a report recommending disciplinary charges against Const. Michael Adams, one of the officers, involved in Manon's arrest.

The Special Invesitgations Unit, Ontario's top police watchdog, accused him and four other officers of using excessive force during an arrest at the G20.