Belleville High School was back in session today after students on Facebook discussed bombing the school, prompting an early dismissal Monday.

The Facebook discussion between four students was was most likely a joke, said Belleville police's Deputy Chief Mark Minichini. But their conversation about blowing up or setting fire to the school landed them in the Essex County Juvenile Detention Center. They were then fitted with ankle bracelets and sent home on house arrest, the deputy chief said.

Schools Superintendent Deborah Perri deferred all questions to the Belleville police department. The four have been suspended from school and face expulsion, according to Minichini.

At about 8:30 a.m. Monday, a student printed out the Facebook conversation, which took place Sunday evening, and gave it to a vice principal. By 11:30 a.m., the superintendent had evacuated the school for the rest of the day.