why would they give him a vest though? to keep him from getting shot?
The vest usually reserved for people who might get retaliated against. We want to the guy to live so he can make it to court so that charges may be brought to him then so that he can make it to jail to await trial. They don't want vigilantes and assassins to kill them and yeah I am sure everyone wants to see him on the ground in a pool of blood, but we are better than that.

Basically to protect them from people who want them dead so that they can live to see a trial