The police are following the stupid rules set in place - for the folks long out of school, this is called Zero Tolerance and has been in place in most US schools for about 15 years now. If you are caught with anything not allowed that's it, end of story. They have intentionally removed the leeway to make an informed decision about things like this.
On the other hand, the outcome isn't surprising, given the inputs -
1. School administrators of questionable intellect following stupid rules made by bureaucrats
2. Brown kid hauls a questionable-looking suitcase with giant LED clock and plugs it in during english class, during which the alarm "goes off" and attracts attention (his goal, or an accident?)
3. English teacher does not have the brainpower or tech background to recognize that it is not a bomb and passes the buck to the admin
4. School police are involved and they try to make an example out of him because they knew who he was, and that his father has ties to foreign countries furthering their doubts (doesn't help this is around the time of the Sep 11 anniversary)
It is an off the shelf alarm clock that he gutted and bolted into an equipment carrier. It has battery backup but it is unclear if he had a 9V battery installed at the time. These clocks typically turn off the display but still run the alarm if running on battery.
Faculty are required by zero tolerance rules to report behavior that might arouse suspicion. So under those rules the first tech teacher was breaking the rules, and the english teacher followed them. 10 years ago in my day some kid did something similar with a Pelican case - except there was nothing in it but foam. He was suspended for a couple days because of a similar kneejerk reaction.
On the other hand I brought in a frankenstein portable video game system and played it at lunch, and even with other teachers. The difference was it looked professional and not like a B-grade movie prop.
Obama extends an olive branch but had the kid showed up at a meet and greet with that clock, Secret Service would be swabbing up the kid's nether regions with an electron microscope.