Kowloon Bay gunman Li Tak-yan once banged violently on almost every neighbour's door to complain about noise, according to a resident who knew him.
And in August 2011, the divorced and jobless man attacked a neighbour when he was living in a temporary housing estate in Yuen Long. He was jailed for a year for slashing the man's hand.
Tales of his temper emerged after a 12-hour drama in which Li, a 51-year-old mainland immigrant, is believed to have shot and killed himself when police surrounded his 10th-floor flat in Lok Ching House, Kai Ching Estate, on Sunday morning. He is suspected of having shot dead a 43-year-old air-conditioning technician, Liu Kai-chung, on the 21st floor on Saturday night.
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Police searching Li's flat have taken away two 7.62mm calibre pistols, one homemade, 43 rounds of ammunition, three knives, three holsters and a computer. They are seeking help from Guangdong police on how the weapons entered Hong Kong and on Li's background.
Li's hot temper was well known even to residents of other floors, said an 11th-floor resident giving his name only as Wong.
"He's not the kind of neighbour who you can have a casual chat with," he said. "About half a year ago, he banged on everyone's door [on my floor] to complain about a noise problem and no one dared to open their doors."
But Li returned to his flat after Wong suggested that he complain to the police instead.
"So he didn't seem to be that irrational to me."
Wong recalled that on another occasion Li gave him "an unfriendly stare" when he was putting rubbish out. That was the last time he saw Li.
A 17th-floor resident, Tsang Yuk, said that when she took her son to the courtyard downstairs she always saw Li wearing the same red polo shirt.
"His shirt stank so bad as if he never washed it," she said, adding that he acted rather strangely and liked to sit in different corners of the playground.
Another resident recalled that Li "walked like a mafia boss" and had a tendency to swing his arms forcefully when he walked in the courtyard.
"But he would sometimes say hello to neighbours so I really didn't expect this," she said, referring to Li's shooting of Liu.
A 21st-floor resident who reported the Saturday attack to the police said he emerged from the lift that night to see Liu lying on the ground. The victim held a key in his hand and had two red spots on his chest. His thigh had another wound.
"I had never seen people being shot before, so I wasn't sure what was happening," the resident told television news reporters. He thought himself lucky that he did not board the lift earlier or he might have been involved in the drama.