How do you get the police uniform without killing anyone and does it stay..

once u get put on the beat patrol and arrest the three criminals go to a clothes store and purchase some clothes go back to the police precint and go to your locker the police uniform should be there but u cant change back into casual clothes because the police uniform will dissapear

Without a Police Uniform, from level 1, The Police Uniform will Dissapear.

If you are like me and you want the police uniform without killing innocent civilians--fear not--for it is possible. First, pause the game and scroll to the ComSat menu. Second, enter the Debug menu by pressing left and IMMEDIATELY pressing L1 and R1 together. If you manage to time it correctly you will see the Music Player screen overlap the ComSat menu. (Youtube a tutorial if you have any troubles, though it is really easy). Third and final, scroll to the "case and mission load" option and set the parameters to "case name: Mission 0" and set the second parameter to "Mission name: Police Precinct Demotion" and the game will force-ably load the intermission sequence that puts you on beat patrol with the police uniform with no innocent lives lost! This is the ONLY other way to obtain the police uniform other than going on a mad blood thirsty rampage.

Enjoy!
Denny Frontier