Jailed beyond their sentences

Two former BYU-Idaho students are being held past their sentences because they're needed to testify in an upcoming trial. The prosecutor thinks they're a flight risk. I'm inclined to go to bat for these two men; they've served their time, and should not be treated as criminals anymore. Also, is it legal for a prosecutor to put a potential witness in jail? I thought it was suspects who were considered flight risks... Kudos to Channel 3 for this story.