A 22-year-old psychiatric patient has been arrested on suspicion of murder after a passer-by was killed by a chair thought to have been thrown from the roof of a 10-storey building in Mong Kok yesterday.
The suspect is a former waiter who had been receiving treatment for mental illness for about six months, a police source said.
"Doctors are assessing his mental state in hospital," the source said. "We will look into the results of his medical examination as part of our investigation."
Salesman Wong Wai-tik, 29, died after being hit by the chair as he walked with two colleagues on Sai Yeung Choi Street South at about 1 am yesterday. He was declared dead at Kwong Wah Hospital in Yau Ma Tei at 1.19am.
The 22-year-old waiter, who arrived from the mainland in 2009, was found drinking beer alone on the roof of the building at No 59 in the same street where he lived alone in a top-floor flat, police said.
He was being held in the custodial ward of Kwong Wah Hospital last night. He had not been charged.
A spokesman for Kwai Chung psychiatric hospital said the man had been discharged from the hospital earlier this year. He had been visited regularly at home by a psychiatric nurse. He had a consultation on Friday and his next appointment had been scheduled for July 4.
Wong and two colleagues - a man and woman - were walking on the pavement opposite No 59 after a meal when he was struck.
Video footage shows him lying unconscious in a pool of blood next to the broken chair. "Don't sleep. Don't sleep, Ah Tik," his distressed female colleague can be heard shouting.
Kenneth Ng Chun-kit, 46, a visitor to Mong Kok, said there was no way people could protect themselves in the streets. "It's just fate and luck," he said.
On the roof where the waiter was arrested, police found a chair similar to the one that landed on Wong along with several empty beer cans.
"Initially, he admitted he had thrown a chair down to the street earlier," Superintendent Jackson Mak Pui-yuen, assistant Mong Kok district commander for crime, said.
Mak said police would check images from a HK$1.7 million "Eye in the Sky" surveillance system to see whether it had captured the incident.
The system was set up in Sai Yeung Choi Street South after three incidents in which acid was thrown down into the street in the pedestrian precinct from December 2008 to June 2009, injuring 101 people.
Police offered three rewards totalling HK$900,000 for help in solving those attacks, but no arrests have been made.
Dr Wong Yee-him, specialist in psychiatry for the Jockey Club Early Psychosis Project, said the man's behaviour appeared to show symptoms similar to schizophrenia and that he might have suffered from a relapse by not taking medicine as required between sessions with his psychiatrist.
He speculated that the man might have thrown the chair because he had heard voices telling him to do so.
Wong said the Hospital Authority had been providing services such as regular visits to psychiatric patients but could not cover all patients because of a lack of nurses.
Chinese University psychiatry professor Lee Sing said Hong Kong was short of psychiatric doctors, psychiatric nurses, clinical psychologists and social workers.
He said a psychiatrist was required to see at least 30 patients in a three-hour morning session in a public hospital.
With only six to seven minutes available, he said it was possible a doctor might overlook or underestimate a patient's illness.
"In fact, they have apparently done a good job, otherwise more such tragedies might occur," he said.
An earlier version of this story misstated that the building was nine storeys tall. It was in fact a 10-storey building.