If I'm talking about a specific police officer, then I'd use "o", which means he/she/it/that.
O geldi -> he/she/it/that arrived.
O polis geldi -> that police arrived.
Ona polis geldi -> police arrived to him/her (his/her place).
polis geldi -> the police (has) arrived.
O bahsettiğin polis geldi -> The police officer you were talking about (has) arrived.