Well, where ARE the witnesses. I just cannot believe nobody EVER sees anything.
You have to figure if you are with someone who just got shot you more than likely will be looking at the victim on the ground more than looking around for the killer. You usually are more concerned about getting help for the victim and by the time your brain registers the tragedy and you go get help which means run back into the restaurant the sniper is long gone.
You have to figure this guy goes into the parking area before he commits the crime and scopes out where he is going to commit it and how he will get away maybe a day or two before. He also makes sure that it is in an area where he can concealed himself from any witnesses.