how is their treatment different from how common criminals are treated?

The common criminal had more freedom. They were often friendly with the guards. The Party was not concerned with Prole prisoners. Prole prisoners have more freedom in prison. They swear at the guards and joke with them. They are able to enjoy contraband items and trade them. Political or party prisoners were tortured and abused. They had no freedoms. They were deemed threat to the party while prole prisoners are not.