Hong Kong police on Tuesday arrested a TV producer who worked for the city’s public broadcaster RTHK. She made two investigative programs about police actions in connection with an outbreak of violence in July 2019.

The woman Dora Choi (aka Choi Yuk-ling) was arrested at her home address in connection with alleged false statements and violations of the Road Traffic ordinance.

The incident on July 21, 2019 in Yuen Long district has become one of the most notorious and bitterly disputed flashpoints in last year’s battle between pro-democracy and pro-Beijing forces in the city.

A gang of men wearing white T-shirts and carrying sticks boarded a subway train in the station and violently attacked passengers. Among the injured were some wearing black T-shirts and who may have been anti-government protesters. The gang members are widely assumed to be triad, or organized crime, members acting as private sector muscle on behalf of the government, though this has not been proved.

Police were called by passengers and bystanders, but it took them 39 minutes to arrive at the scene. That is an unusually long time in the small and densely populated territory, and democrats subsequently alleged police collusion with the mobsters.

Choi’s documentary pieced together a narrative using video footage from nearby shops, the tracing of car number plates, and interviews with locals. She showed that plain clothes police officers were in fact on the scene before the violence began.

After the program aired on RTHK, the police admitted that the under cover officers had been in the town to “observe the situation.” But in August this year, the police published a completely new version of events, one that they described as a riot and as a fight between two “equally-matched” sides.

RTHK, which is technically a government department, has come under repeated attack in the past two years over matters including the protests, satirical programming, and relations between China and the World Health Organization.

Junius Ho, a member of member of Hong Kong’s Legislative Council, was filmed in the Yuen Long area apparently greeting the white shirted men before the incident in the station. He denies any wrongdoing.

Ho was recently named chairman of as chairman of Legislative Council’s IT and broadcasting committee. On Friday, one of his first pronouncements was to propose the merger of RTHK with the government’s public relations unit.

Pro-democracy legislators have been quick to condemn Choi’s arrest. Council Front lawmaker Claudia Mo, a former journalist, called the arrest a blatant attack on press freedom.

“The police operation will inevitably create a chilling effect that those journalists who dare to report any wrongdoings of the government officials or the pro-establishment camp have been facing great pressure and I urge them to stand firm and report the truth… without fear or favor,” said another, Lam Cheuk-ting, who was among the injured in Yuen Long.