It's possibly an oblique reference to one Lord Greville Janner, who was accused of child abuse by numerous witnesses, but was spared a trial because of advanced dementia - even though he'd been voting in the House of Lords and attending committee meetings.
Tragically, Janner died not long after he was declared unfit to plead. Even more tragically, it was decided the public interest would not be served by a trial of fact which would put evidence from witnesses and alleged victims on the record without aiming for a conviction.
Translation: someone who can't be put on trial.