keep (someone) on ice
1. To postpone or delay acting on or interacting with a person. I know that journalist has been persistent in getting a comment from us for his story, but we'll just have to keep him on ice until the trial is over.
2. To detain or confine a person in isolation, especially before or during the course of interrogation or torture. The group kept their prisoner on ice for nearly a week before beginning their interrogation. We're keeping the snitch on ice until the boss decides what to do with him.