"plunge" has connotations of diving in deeply with speed which suggests that the coplaunches himself into violentsituations with little regard to consequences.
"two hieroglyphs on his face that mean trouble" just as hieroglyphs are an ancient Egyptian language that is hard to decipher and understand so the cop is unpredictable and difficult to read as a person.
"Built like a gorilla" just as a gorilla is a violent, uncontrollable, large animal so the cop is a big, intimidating figure.
"thin tissue over violence" just as a tissue is a material that is easily broken with little to no effort so violence could break out at any moment without warning.
"he hoped it, he truly hoped it" is written in the technique of repetition. This puts emphasis on the fact that the cop has a very dangerous job and he might not return home one day.
"And who would be who have to be his victims" the technique used is a rhetorical question which helps to show that people don't have a choice whether or not to be swept up in the violence, they either are or they aren't.
"Nightstick" has connotations of weaponry and arming which suggests the cop is even more dangerous when he is in the possession of a weapon.
"Victims" has connotations of helplessness and vulnerability which suggests those who counter the cop don't have a choice whether or not to be envolved.