Questions re penultimate ep - SPOILERS

(I take advantage of every opportunity that comes my way - and there are few - to use the word "penultimate.")

I've watched all but the series finale - no spoilers on that, please? - and have two questions.

In the second-to-last episode, Cedric and Ronnie go to the evidence locker, where he uses a number she has in a file to call a cell phone (which had been booked as evidence) from his own. If their expressions when the phone rang were supposed to "tell" us something, it got past me. I thought this was probably Marlo's phone/number, but why was Cedric checking this out - and on the down-low - as Freamon had confessed his plan to him?

When Mike drives Duke to the stables after taking Bug to his aunt's, he disapproves of Duke's involvement there, saying he knows what goes on inside - but I don't understand why? I guess they must've been doing something worse than stealing scrap metal?

TIA.