A police officer who had part of his thumb sewn back on after it was hacked off by an attacker is to have it removed again after surgery to reattach it failed. Constable Li Kin-chung, 36, suffered the injury when mentally ill Cheung Chee-yung, 49, went berserk in his Tsuen Wan flat on Sunday. Cheung died on his way to hospital after being subdued by officers using batons, riot shields and pepper spray, but the cause of death is still unclear. A police spokesman said yesterday Constable Li would have to undergo surgery to remove the reattached section after doctors found the first operation had been unsuccessful. He said compensation would be settled after the officer recovered. Constable Li's boss, Superintendent Phil Woolcott-Brown, said it appeared Cheung, who was armed with a chopper, severed part of the constable's right thumb as the officer tried to use pepper spray to control him. Mr Woolcott-Brown said police could not get a full account because the officer was still in a serious condition in Princess Margaret Hospital. Constable Li was one of six officers who went to the flat in Ho Pui Street. Three other officers were injured in the incident.