He's not in prison, he's in jail, and there's a big difference.
What?! Jail and prison are synonyms. There is no real difference.
http://www.oxforddictionaries.com/definition/english/prison - A building to which people are legally committed as a punishment for a crime or while awaiting trial.
http://www.oxforddictionaries.com/definition/english/jail - A place for the confinement of people accused or convicted of a crime.
Both refer to being detained both before and after conviction.