[grey_whiskers]

Law enforcement uses hand signals to communicate in many situations.
Uniformed-cop-on the-staircase landing is verifying the shooter was fellow law enforcement instead of just opening up on him.

[norsky]

Law enforcement uses hand signals to communicate in many situations.

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Something for your kitty collection, not related to your post btw

[Steven W.]

How would one know that? As I recall the shooter was not uniformed