Murdered criminals have had all of their fingers lopped off. The digits are shown laying on the floor/ground and the fingerless hands are shown. Not a lot of blood shown, though.
There's lots of dirty police. You see lots of bullying and violent behaviour. Even those who are supposedly positive characters do dodgy things and make stupid choices. I wouldn't say this is in any way supposed to portray the police in a way to make you think they are amazing. At best, the message is that they are normal people who make stupid decisions.
A character is mentioned to have had an abortion at the end of season 2, when her medical records are accessed. It's hinted at in a previous episode as her "getting rid of a cat"
Someone refers to another character with learning disabilities as r****ded. It happens in the first ep of s4 but is shown again in the "previously" opening sequences.