With the long history of China, comes a long history of secret police organizations. The Police Bureau mentioned here was an organization more or less created by Lai Junchen during Wu Zetian’s rule. The place, located near the Lijing Gate, was a prison for major criminals.

The Police Bureau, from what I understood, meant a prison rather than some kind of secret police, but in effect Lai Junchen utilized a wide framework of several hundred informants to discover dissidents and/or frame unfavorable people.

There aren’t a lot of mentions of the Police Bureau, and none outside of the context of Lai Junchen’s activity as an official, so I think it might have ceased to exist with Lai Junchen’s execution, but don’t quote me on that.