has he recently had a big stressor or stressors in his life? Usually that can cause kids to regress on things such as potty training.
I agree with RockRose, This one incidence could not have led to him being expelled from school and technically they have to provide you with some options. You might have to send him to another school, but he has to get an education.
Bijou, have you looked into encopresis as an explanation for his bowel movements? You need to solve that.
Is he in private school? The reason I ask is because in public school, to expel a child they have to have a very long documented list of very difficult behaviors, and document that they've done everything they can to solve these issues.
What changes have there been in his life recently that would explain his angry outbursts?