Two other men emerged from a stairwell and Dr Leung knew something was seriously wrong.

They tried to force Dr Leung into a wooden box, but he fought his attackers and, in desperation, bit off one of their fingertips.

'He realised he was in great danger and resisted as hard as he could,' senior counsel Arthur Luk Yee-shun said yesterday.

Those assailants have never been identified. But two other men - Brandi Chiang Sai-wah, 48, and Jimmy Wong Hon-wai, 32 - were key players in the botched kidnapping on November 6, Mr Luk said during his opening address at the pair's conspiracy trial.

Chiang - the younger brother of former Kowloon City district councillor Chiang Sai-cheong - was the organiser who tracked down a box to transport Dr Leung, the court heard.

He also allegedly procured an oxygen cylinder for the kidnappers' planned captive.

Wong, a truck driver, was paid HK$1,000 to wait for his fellow kidnappers and transport the box to the group's hideout, a rented pig farm in Yuen Long, the prosecutor said.

Both men have pleaded not guilty to a charge of conspiracy to commit forcible detention.

Meanwhile, jurors were shown the foam-lined wooden box while victim Dr Leung, commonly known as 'Dr Toilet' because of his past campaigns for clean public facilities, briefly testified, confirming that he was the man caught on surveillance cameras riding in the lift with a still-unidentified person.

Later, Tso Yiu-chuen, Chiang's friend, testified that the accused mastermind asked to borrow his car just days before the kidnapping attempt.

Tying pieces of evidence - including packaging for the box and oxygen tank - to Chiang's residence would prove his guilt, Mr Luk said.

The court would also hear that a man calling himself Mr Lee, who had the same phone number as Chiang, called a medical company to ask about renting an oxygen cylinder.

A witness would testify that a person also using Chiang's phone number rented a van to transport the box.

The landlady at the farm was expected to say she stumbled on a key piece of evidence when she checked on her new tenants, Mr Luk said.

'She couldn't find [her new tenants] but she noticed that a large wooden box ... was placed in the dining room of a house on the pig farm,' he said, adding that police later found a bag used to hold oxygen cylinders at the farm.

The case against Wong would rest on his police interviews, during which the truck driver played down his involvement, Mr Luk said.

'He told the police that he didn't know he was involved in something so serious,' the prosecutor said. 'It is the prosecution's case that [Wong] was not entirely honest with police.'