There have been too many changes too soon.
HAve you discussed at length exactly what happens when he goes to school? Who he will sit by, where his lunch comes from, where he sits for lunch, where the bathrooms are.
Who are his allies in school? I'm guessing he doesn't have any right now. New area, new kid, homeschooled kid back in public school, OCD, anxieties, yadda yadda, the list goes on.
So first get to the pediatrician and have him referred for an evaluation by a professional.
Can you homeschool him for the time being?
Get him onto a tight schedule, start at 8, do 1 hour of math, 1 hour of English, 1/2 hour spelling or whatever.
Make mealtimes healthy, no empty calories
Let him know the plans, repeatedly. You will have to reiterate what happens and what he is to do when it's, let's say, lunch time. You will go with teacher in a line to the lunch room, you will go to the hot lunch line, you choose which hot lunch and which side, you will sit HERE with the other students from your class. You will throw your garbage here, then you will line up and go out for recess.
Do the same with the teacehr's schedule.
I took my daughter out at 5th grade. She had terriblle anxieties. In 4th she was still throwing up at school and wetting her pants. She is finally ready to go back, it's been 4 years. She'll return to school as a freshman and she is ready.
Sometimes we have to look real hard at what we are doing to our child. Is school the best place?
And do not call police. He has a disability, OCD and anxiety. He is frightened. His world has come unglued and he has no way to control it. Help him learn to control what he can.