Quinn suspected dexter killed liddy.
Quinn sees the blood dripping from the car when miami metro visits the scene so he pry suspects the blood on his shoe is.
Webin season 5 of dexter, detective joey quinn is heavily suspicious of dexter and what he gets up to.
Joey then hires liddy to spy on him.
Liddy gets some good.
Webhowever, what i don't like about the aftermath of rita's death is quinn's immediate suspicion of dexter being the killer.
It's completely normal to suspect someone close to.