[Rob!]

Don’t worry, I’m not planning on doing one myself.

It’s for my next book. The main characters (one of which is a detective sergeant) are walking through the town when a gun man suddenly starts shooting from a multi story car park above them.
Can anyone help with what the police actually do in a situation like this? If it helps, it’s not a terrorist incident (though I would imagine that it would be treated as such until they know otherwise).

Thanks in advance