"Some lawbreakers may mix into the public meeting and procession to disrupt public order or even engage in illegal violence," the police warned in their letter.

Source: https://gazette.com/news/us-world/hong-kong-police-keep-tight-tabs-on-first-authorised-protest-in-years/article_dfdc75fd-dda2-5f01-b45c-653b2a47e175.html

“The lawbreakers began shouting incitement calls, firing firecrackers, and throwing objects at the police officers who were operating at the scene,” the statement read.

Source: https://www.canindia.com/al-aqsa-mosque-witnesses-second-day-of-violence/