Actually, there's a more sophisticated method; he doesn't need to hire gangsters to impersonate the criminal police.
But the situation was sudden, and Fushimi Roku didn't have much time. He needed to quickly stir up conflict and ignite the anger of the vast majority to proceed with the next step of his plan.
The radio keeps broadcasting reports as it receives the police's internal radio line. A system alert pops up in front of Fushimi Roku, showing the number of instigators is constantly rising.
"Everyone, this is an emergency broadcast from the Police Department..."
Fushimi Roku heard the broadcast: the police criminal division and the riot squad are urgently mobilizing.
"Is it about to begin..."
...
By the time the criminal police from Search Division 1 arrived at West Sugamo, the situation was already out of control.