[sandworm101]

The procedure involves jailing someone under a false name, at least on the paperwork. It isn't that unusual and is normally used in organized crime cases. The arrest is done under the guise of arresting a "material witness" rather than an accused criminal. Doing this bypasses various protections (lawyers, hearings etc) for a significant period of time. The use of false names is to protect the "witness" from intimidation. The suspect is then re-arrested on criminal charges while in custody once the need to keep him secret is over.

An infamous case: https://en.wikipedia.org/wiki/Brandon_Mayfield