All police departments use RWD vehicles.
I know that one reason police cars use RWD is that they are easier to repair after front-end accidents. Front-wheel drive autos have a lot more problems after running into things. Police cars tend to get a lot of hard use, which front-wheel drive cars can't handle too well. When a car is accelerating, the front is lifted, sometimes even off of the ground. RWD would allow the powered tires to maintain in contact with the pavement.