I don't like the advise the police give out 'call the police if the deer is injured" if you've hit a deer badly enough that it can't get away all your doing is prolonging the suffering.

That advice is because most people can't dispatch a wounded animal in the UK (both technically and legally), a friend of mine is a Gamekeeper and he hit a Roe deer on the main road outside the estate he lives and works on and had to call the police to deal with it who called out a vet and in the end someone was called out to shoot it...

He had just finished teaching a DSC course and had a rifle and ammunition in the back of his car, but it took over a hour for them to show up and when he offered up that information (poor thing had crawled onto his estate and past the 50ft disturbance line) he had to explain to the officers and the armed response officers (who he knew) he had to wait for another few hours to get cleared to drive off the half mile to his home.