I would also stop as acourtesy"backup" in situations and areas where I deemed 
necessary. The officers were "aware" of the extra car and due to lack of 
communications he knew "someone" was there but not exactly who. Sometimes a 
flash of badge as necessarybefore officer concentration was totally broken.
I know at least one East St. Louiis officer who was shocked to have an 
unknown white guy help him in a stop where he had bitten off more than he 
could chew.He had NO backup at all that would help him.  Not uncommon there 
to see one of theor own unfavorite officers left hung out to dry.
--- Maximus 3.01
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