That doesn't matter at all. He wrote a song about a convicted cop killer he believes is innocent, therefore, he is the anti-christ. Also, rap sucks, almost as much as the Sharks.
He read no such "poem" at the event. The poem he chose to read was an inspirational one about overcoming hardships in the hood. "Cop killing" was never even broached by Common or even mentioned by the him or the White House until it became an issue for the right-wing media to rally over.