During Watergate Butterfield was whisked to testify without a subpoena

[blogslut]

1. I may be wrong but

Butterfield had already revealed the taping system to committee staff investigators during a non-public question session before his public testimony. Dean had wondered about the possibility of taping and some other stuff happened that had the committee looking for evidence of it. Butterfield would never had told them about it if those staff investigators hadn't asked him about it.