I've had another one of my totally off-the-wall ideas about this case. Please forgive me, I have way to much time on my hands some days for just thinking about this sort of event.
Apologies too to the witness for continually dragging him into various positions in the scenario. If both he and Mr. Al_Hilli had more discreet careers than the obvious, could they have been meeting during those trips that Al_Hilli was taking from the campsite, possibly to discuss someone else who was staying there? It's possible that they had planned to leave the area after this meeting, so he brought the family and their bags along. While there were sitting there waiting for the "contact" to get there, the shooter ambushed them, killed them and the French cyclist, thinking he was the one they were there to meet.
Judging from the description given of the gun, I'd have to change my original theory on the shooting of the young girl (sorry, I'm terrible with names.) It seems more likely now that he had emptied the weapon on the family, but the girl wasn't seriously wounded. Rather than reloading immediately, he hit her in the head until he assumed she was mortally wounded, and then reloaded just in time to shoot the cyclist. The last I heard they found 25 casings, they believe the gun could hold 20 rounds, and the cyclist was shot 5 times.
I really hope I'm way off on this theory though since it would mean that the witnesses, especially the other cyclist could still be targets.