Some may recognize this name from Metal Gear Solid. I'm sure you can see soon why I chose this name because anything and I mean anything can kill you in 2/3 shots!

The police has a bullet proof armor on, the only way to kill them is a headshot. 
Note: In the mission Reuniting the families the cop that jumps on the car cannot be headshot, so change the pedstats of STAT_COP the defense rating (I value) to 0.1 for that mission. After that change it back.