No spoilerz please, but.
At the end of episode 3 or 4, McNulty met the FBI guy in the car-park to ask whether they could get wires.
He told him they couldn't give them to the investigation because the feds had dirt on Lt. Daniels.
How come no-one cares about it? If it's part of the story and is revealed later, don't tell me what it is, but does it matter to the plot or was it just a little aside which doesn't get any follow-up?