The acrimonious relationship between Hong Kong protesters and police took a turn for the worse on Tuesday night when an undercover police officer disguised as a protester was caught on video behaving in a highly belligerent manner toward bystanders.

Protesters accused the police of attempting to infiltrate and sabotage their movement with such tactics.

The Hong Kong Free Press reported the video of the undercover officer’s antics quickly became a viral sensation:

Sheung Shui station was closed at 8pm on Tuesday. But the videos, shot at around 11pm, showed a man in a hat and a scarf inside the station. In one video, the man pointed a finger at people outside the station shooting videos and told them to leave. When asked why he was inside and why he hid his identity, the officer took out a flashlight and aimed it at the person shooting the video. “Why does it look like a flashlight that police use? I am just here to have late night food. I am just passing by,” the person who shot the video said. In a second video, the officer took out what appeared to be pepper spray and pointed it at those outside the station.

Hong Kong police officials confirmed the presence of plainclothes officers in the Sheung Shui station on Tuesday night, purportedly to “carry out an investigation.” The MTR railroad corporation said it also had security guards posted in the station.

“All police officers certainly will not break the law. The police will continue to make use of different methods to combat crimes according to operational needs,” the police department insisted.

These statements were challenged by citizens posting on the department’s Facebook page who asked how the officer could justify covering his face and threatening bystanders with pepper spray, especially since Hong Kong chief executive Carrie Lam invoked emergency powers to make masks illegal last week.

“Were they conducting a mission to damage the station?” one commenter wondered.

Ever since the first known deployment of undercover officers, there have been questions about whether they were acting as agitators in order to discredit the movement and goad real demonstrators into taking actions they could be arrested for.

The conduct of undercover police officers has frequently been criticized by protesters, including incidents where undercover officers suddenly revealed themselves and used unjustified levels of force against demonstrators. Arrests made by undercover police have been exceptionally brutal, in part because protesters thought the officers suddenly appearing in their midst and manhandling them might have been thugs or gangsters and responded fearfully.