Does Chicago Mayor Rahm Emanuel have KNOWLEDGE about a possible police coverup?

No he didn't know. No politician knows what's going on when it gets to their desk. Normally there is a fall guy on hand to take one for the team knowing he'll be well compensated on the back end. So it's possible he "didn't know" (wink wink). It's happened lots of times. Recent would be Reagan and LTC North, Bill Clinton and Monica (she got free macadamia nuts and cigars), Bush Jr and GEN Powell and some would wager Obama and EVERY Flag officer since he took over as POTUS. Even DS backbone is even like WTF? It's going to happen again with the next president or politician statewide.
I'm more concerned how some cops go through proper training at their academies and just throw it away when they get to the streets. Not all are in this boat and even then to me 95-99% of them are honest folks. What brings them to the point where they can so easily take a life and know that the line will be there to protect them until the bitter end, even when it's blatantly wrong what was done.

Without a doubt he knew or assisted in keeping this out of the public's eye. You have to remember, while this is current in the news now, this incident occurred a month after the shooting of Brown in Ferguson.

The bus may be running late (because the police chief was under it) however its still making one more stop at Rahm Blvd.