Hong Kong police on Saturday said they had foiled a second bomb plot in under a week related to the ongoing anti-government protests after officers arrested three men allegedly testing home-made devices and chemicals in a secluded area.

The suspects were testing the strength of remote-controlled devices, which were intended for use at mass protests, police said, but it was unclear which chemicals or explosives were involved as the bombs had been detonated.

Acting on intelligence, officers from the organised crime and triad bureau ambushed the trio in scrubland off Siu Lang Shui Road in Tuen Mun in the early hours as they carried out tests.

The operation came as police said three men and two women, aged 15 to 18, had been arrested in suspected connection with the death of a 70-year-old man who was hit by a brick during a fight between masked protesters and Sheung Shui residents last month.

According to a source, police were seeking legal advice on whether the “joint enterprise” principle, which allows for accomplices of the person who strikes the fatal blow in a murder to be convicted of the same crime, could apply. CCTV and online clips did not show the five throwing bricks directly at the man, but some did throw bricks and wound others, the source said.

In the Tuen Mun operation, officers also seized a radio-controlled detonation device and protective gear, including shields, bulletproof vests, a steel plate and gas masks at the scene. The tools were believed to have been used during the tests.

“The amount [of explosives] was not a lot. But intelligence showed there were two purposes behind the plot – one was to upgrade the power of the bombs, and the other to launch attacks at future assemblies or rallies,” Senior Superintendent Steve Li Kwai-wah said.

The suspects were also testing chemicals and officers would collect soil samples, he added.

“This worries us a lot … because many hikers also passed by today. It posed a great risk to the public,” Li said.

According to Superintendent Suryanto Chin-chiu from the bomb squad, officers found a transmitter and a receiver at the scene and believed the devices were used to detonate the bombs at short-range using a low frequency.

Earlier in the week, police defused two powerful home-made bombs in Wan Chai. Suryanto said the detonation method in both instances was the same, but the electrical parts inside the devices were a bit different.

“As the suspects [arrested on Saturday] were just testing the chemicals, we found a small area, 4 inches by 5 inches, that was burnt,” Suryanto said.

He said a tiny amount of chemicals and explosives were discovered on the trio, and that the devices were not easily found in the market.

“We believe they were testing whether the explosives were functional.”

The trio were arrested for causing an explosion likely to endanger life or property and detained for investigation.

Li said they had an active role in the plot, including building the bombs. But he refused to disclose if the suspects had previously taken part in anti-government protests, or if they had professional knowledge about bomb making.

“They had prepared protective gear during the testing, meaning they didn’t even know the power of the bombs,” Li said.

A senior police source said one of those arrested was a 27-year-old laboratory technician from SKH St Simon’s Lui Ming Choi Secondary School in Tuen Mun while another man, 40, worked as an electrician. The third was unemployed.



“Our investigation suggests the latest bomb plot is not linked to [the earlier] bust,” he said.

Officers in the evening escorted one suspect to the school as part of their investigations.

Separately, police said on Saturday they found 34 petrol bombs, 20 smoke bombs, 12 corrosive bombs and a number of easily flammable items after receiving a call from City University staff about suspected dangerous items on the Kowloon campus.

The university also discovered dangerous chemicals on campus last Friday, which were disposed of by police’s explosive ordnance disposal bureau.

On Monday, police seized two powerful home-made bombs, packed with 5kg (11lb) each of high-grade explosives along with shrapnel in the form of nails, at Wah Yan College Hong Kong in Wan Chai.

Detectives believed they were intended for an attack the previous day on police at a massive anti-government march, which around 800,000 protesters attended.

It was understood the remote-controlled devices – which officers said had a potential blast radius of up to 100 metres – would not have gone off where they were found, because two mobile phones connected to them, for use as detonators, were turned off.

The apparent bomb plot, which emerged after six months of social unrest and political turmoil, prompted the city’s biggest police association to warn that the security situation in Hong Kong was at its “most alarming” in decades, even worse than during a wave of armed robberies in the 1990s.

Meanwhile, dozens of people joined a rally on Saturday night calling on Britain’s newly elected parliament to consider terminating the 1984 Sino-British Joint Declaration, the agreement that paved the way for the city’s handover in 1997, because Beijing “had violated declaration promises including ‘one country, two systems’”, but the crowd was smaller than at a similar rally held on Wednesday.

Activists said the rally, held outside the British consulate and organised by the Hong Kong Independence Party, was held because at least two Conservative Party MPs who supported their cause were successfully elected in Thursday’s general election.