From season 3 episode 2. McNulty is unhappy with some crime report on the suicide of D'Angelo Barksdale. This is what he has to say:
The troopers really fucked the pooch on this one. All I have is some half-assed report. Reads like the investigator went off his Ritalin.
A lot of what happens seems planned by people who went off their Ritalin. Just if you are need of an explanation.