It was the second protest since Keith Fong Chung-yin, 20, who heads Baptist University’s students’ union, was arrested by five off-duty officers at around 7.30pm on Tuesday, after he spent HK$4,200 (US$536) to buy 10 of the pointers from a stall in Apliu Street, Sham Shui Po.

More than 1,000 protesters, including students from the university, besieged the Sham Shui Po Police Station on Tuesday night, and officers later fired about 20 rounds of tear gas to clear the crowd, who sprayed paint on the building’s walls, and hurled bricks and glass bottles into the complex.

Police arrested eight other people during the clearance operation, including another Baptist University student, Chan Ka-shing, for offences including unlawful assembly and obstructing police officers in the execution of their duties.

As of Wednesday night, Fong remained detained at the Caritas Medical Centre, where he was sent after complaining of feeling unwell. Chan was released on HK$500 bail (US$64).

Baptist University’s president, Roland Chin Tai-hong, wrote in a letter to staff and students that “the latest police actions have caused widespread public concern”, and urged the government and law enforcement authorities to respond positively.

Chin, who also went to the tear-gassed protest scene to appeal to other students to leave for safety reasons, said help would be provided to Fong and Chan, who are both first-year European Studies students.

At 8pm on Wednesday, hundreds of protesters gathered outside the museum in Tsim Sha Tsui, with some shining their pointers at the museum, chanting slogans such as “liberate Hong Kong, a laser pointer revolution”, and singing songs like, I Am Angry, by the now-defunct rock band Beyond.

Participants were also heard mocking the police’s claim that the pointers were offensive weapons, saying: “Is the building on fire yet?”

Police defend arrest of Baptist University student leader for carrying laser pointers

Some urged people not to shine their pointers at nearby hotels or at planes.

A 40-year-old participant, who gave his name as John, said it was “ridiculous” that Fong had been arrested.

“The police cannot just arrest him for what they think are offensive weapons,” he said. “There is no evidence that he was planning to attack someone.”

Pinky So Mei-yan, 52, a clerk, said Fong should only be arrested after he had committed a crime, such as using the pointers against officers.

In a press conference on Wednesday afternoon, Chief Superintendent John Tse Chun-chung of the police’s public relations branch warned that the beams emitted could cause “flash blindness” and serious injuries to eyes, adding three officers had needed treatment after demonstrators pointed laser beams at them in recent protests.

A police officer used one of the 10 laser pointers Fong bought to show how it could burn a paper within seconds, after pointing the beam at a fixed spot on the sheet one metre away.

Hong Kong’s justice department denies prosecution of protesters is politically motivated

Democratic Party lawmaker James To Kun-sun and academics questioned whether police had enough evidence to prove Fong’s motives and arrest him for possessing offensive weapons.

Senior Superintendent Steve Li Kwai-wah, of the Organised Crime and Triad Bureau, said Fong had failed to adequately explain why he bought the pointers, and tried to escape when questioned by off-duty officers.

A video clip taken by a witness showed Fong explaining after he had been arrested that the laser pointers would be used for stargazing.

When asked whether the police’s experiment, which could put the suspect in a disadvantaged position during the trial process, was proper, Li said: “I did not smear him or say what it is used for. I just described the power this laser gun can reach” He added that the demonstration would not be submitted to court.

According to the Public Order Ordinance, an offensive weapon is “any article made, or adapted for use, or suitable for causing injury to the person, or intended by the person having it in his possession or under his control for such use by him or by some other person”.

The police did not detail the brand and specifications of the seized laser pointers, and said the packaging provided no relevant information.

Meanwhile, hundreds of students, alumni and staff attended a rally at Baptist University on Wednesday evening to voice support for Fong.

A total of 45 professors and staff, and close to 500 students and alumni, also signed two separate petitions to condemn the police’s arrest.

Bruce Lui Ping-kuen, senior lecturer at the department of journalism, said it was dangerous for the police to presume Fong’s motives.

“The basic assumption of law in Hong Kong is that people are presumed innocent,” he said. “If laser pointers can be sold at the shop, it should be legal to buy and own them,” he said.

Additional reporting by Rachel Yeo