@anemone which one specifically are you talking about?

The most notable one to me was the 1999 WTO protests in Seattle, police infiltrators got caught.

More recently I saw declassified video from the Jan 6 thing and, police were kettling protesters, there was a camera at a guarded door blocking people in, multiple people came up to the door and were pushed away but some of the protesters showed something to the door guards and were immediately let out lol