I'd argue that separating the prime murder suspect from a student population isn't denying him "life, liberty, or property". He has a right to a public education. AFAIK, there are no specifics as to how he receives that education guaranteed to him in the constitution. (Which if he was not a US citizen I'm not sure even applies). The only one of those that could even potentially be applicable would be liberty, but again I don't think there are firm parameters on what constitutes "liberty".
I guess they could fight that out in court? Had he been forced to get his education privately, away from other students maybe a lawyer would argue he was being deprived due process and his right to liberty infringed on? And the other side would argue he was not.