Mass Murder at a High School in Oxford township, Michigan

If I were a perp and wanted to to go on a killing spree the optimum target would be a place where everyone is unarmed and a Gun-Free-Zone would be very high on the prospect list.

First step, get rid of the "Gun Free School Zone Act" and it's state equivalents. The "modified" version STILL makes it illegal for an off-duty police officer to be armed within 1,000 feet of a school, unless he has the senseless duplication of a state issued CCW in addition to his badge and ID.
"Acceptable" CCWs issued by the state where the school is located are the only CCWs honored by the GFSZA. If your out-of-state CCW is honored by the home state of the school, it does not matter to the GFSZA. It is as if you had no CCW at all. The same goes for LEOs legally carrying under the provisions of the "Law Enforcement Officers Safety Act". They violate the GFSZA if they are armed within 1,000 feet of a school zone.
Those "acceptable" local state CCWs? They are only valid under GFSZA if a law enforcement agency examines and approves the application. I question if Florida CCWs are "acceptable", since they are issued by the Department of Agriculture & Consumer Services.

Second step, allow faculty and staff members (with proper training) to be armed on school grounds. Their existence should be well-advertised. Their identity should be unknown.

We can enforce laws requiring gun owners to adequately secure their guns!
Send the parents of this kid to jail.