Four times, a man threatened to hurl a Molotov cocktail at police officers who approached him at his flat. He finally did on May 28 last year, throwing a bottle of flammable liquid with a burning cloth wick at a police officer's shield. Lai Yew Han, now 37, was then arrested.

In court, Lai claimed the incident was an "unfortunate misadventure" and an "accident". He claimed he wanted to throw the bottle outside, but the officers were in the way.

Before sentencing him to seven years' preventive detention with three strokes of the cane yesterday, District Judge John Ng addressed Lai, saying: "It was clear that you are a menace to the safety and security of those around you."

Following a three-day trial, he was convicted on July 7 of one count of attempting to cause grievous hurt to the policeman and four counts of criminally intimidating other officers. Preventive detention, which can last from seven to 20 years, is reserved for recalcitrant offenders. There is no reduction for good behaviour.

The court heard that Lai has been in prison previously for drug trafficking and assault.

Deputy Public Prosecutor Tan Wen Hsien said that at around 5pm on March 27 last year, police turned up at his second-storey flat at Block 66, Marine Drive after a 999 call.

Lai separately showed two officers a Molotov cocktail and threatened to use it. In the first incident, Station Inspector Foo Chuen Chong grew concerned that Lai would throw the bottle at him and went down to the void deck. At 6.45pm that day, Inspector Royce Kiang Heng Hui turned up and Lai made the same threat. Court documents did not say why Lai was not arrested then.

On May 28, police received another call about Lai.

Staff Sergeant Muhammad Shaiful Rizal Ibrahim and Sergeant Guay Zheng Xiong arrived at the scene and Lai made the same threat again. He repeated it when Sgt Daniel Kwok Wei Jie turned up later, but as the only Divisional Tactical Team officer trained to use a shield, he approached Lai, who then threw the lit Molotov cocktail.

Lai, who was unrepresented, said he would be appealing his case.