While there is still speculation about Mateen and his history, here are some links for your perusal. I tried the link posted on the Drudge front page but it was no good. Probably thanks to DHS or one of the other alphabet agencies keeping us safe from the truth.
Read and decide for yourself. Personally, I became convinced that the DHS was full of radical Muslims a long time ago. Little big O has been stacking the intelligence and law enforcement decks with his terrorist buddies since his first day in the offal office.