Sam is absolutely right about why this happened. Throughout the Islamic Middle East, men and women are taught to be opposed to pleasure, especially of the sexual variety. Men are raised not only forbidden to touch women, but to even look at them. Sex before marriage is not just a sin -- but a criminal offence. It is punishable by a severe beating at best, and an execution at worst. This repression often leads to violence against westerners who enjoy the freedoms, including sexual freedoms, that many Muslim men are denied.
Something similar happened at Blacks Beach a few years ago. They didn't come to the beach with guns, but they threatened and harassed many couples and women. I was one of the beachgoers who called the lifeguards and police, who responded fairly quickly and took them all away from the beach. I don't know if they got charged with anything, but it was a scary day.
My main concern is that they were fully intent on going to Deep Creek to kill campers ie naturists. I'm sure all of this will come out as new information and motive are obtained.