Well, he's dead, and may not have been carrying ID, and if he was, it could be fake.
And, hate to break it to you, but you can't tell if a dead person with no ID is an Arab by looking at them. Heck, Sephardic Jews are basically indistinguishable from Arabs, as long as they're dressed the same. How do you think so many suicide bombers get into crowded Israeli locations?
And you'd be hard pressed to distinguish most from some southern Italians, Greeks, various Hispanic groups, etc.