The police have admitted they did send plainclothes officers to Yuen Long where a group of people dressed in white gathered ahead of an attack at Yuen Long MTR station on July 21 last year.
The force made the announcement after RTHK's "Hong Kong Connection" programme reported that a man suspected of holding a police warrant card appeared in Fung Yau Street North, but didn't take any action.
The force has now said plainclothes officers were there to observe the situation and for risk assessment.
A spokesman added that detectives have never stopped their investigation, and have vowed to get to the bottom of the matter.
So far, 37 people have been arrested in connection with the rampage, with seven charged with rioting and other offences.
But the police have been accused of colluding with triads, with officers turning up at the scene only 39 minutes after the attacks, which left dozens of people hurt.
The police watchdog has since cleared the force of collusion.
Last updated: 2020-07-16 HKT 08:36
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