If you want civvies and police to be enemies always, and you don't have east and west in the mission, or if you do .... well, you'll get the idea.
Group the police under a West group leader. In this leaders' init field write
deleteVehicle this
Group the civvies under an East group leader. Write the same thing in his init field.
Or use side Resistance, if that helps.
Oh, and
Welcome to the forum!