A police officer has been found guilty of misconduct in public office for failing to stop two colleagues from physically and sexually assaulting a man while he was tied down on a hospital bed.
CCTV footage had captured the two officers slapping the man's face, prodding him with batons, and punching his genitals.
Au Kwok-wai, 26, and Tang Man-him, 25, who took part in the attack, pleaded guilty to misconduct.
Lam Yik-sing, 31, denied misconduct but was convicted on Friday at the District Court.
The judge said Lam had deliberately neglected his duty by failing to stop the assaults.
All three officers were remanded in custody ahead of sentencing on December 18.
The victim, Chung Chi-wah, 62, was arrested in June last year for injuring an officer and a bystander in Sheung Shui while he was drunk.
He was taken to a psychiatric ward in North District Hospital where the attack took place.
Chung, who was later given a six-month prison term after pleading guilty to assault, said the police violence had left him with a torn ligament in his hand, multiple bruises, and bleeding from the mouth.
Former Democratic Party legislator Lam Cheuk-ting, who has been helping Chung and his family, said they are also planning a civil claim against the officers for compensation.
"Police brutality has been much worse than in this case, but we don't [usually] have sufficient evidence like this time," Lam said, referring to the CCTV footage.