[NegativeK]

> stripped of rights

They're not being stripped of their rights; they're acknowledging that what they're about to say can be used against them.

Waiving rights is common in American law. Open source licenses waive the right to sue; the third-party doctrine waives the right to privacy of the data that companies take. To some extent, liability releases for participating in dangerous activities waive the right to hold the company you're paying responsible -- think climbing guides, race tracks, sky diving outfits, etc. But from what my non-lawyer self understands, there are some rights you can't waive, like the right to sue over gross negligence.

In this case, it sounds like that waiver was used more as an intimidation tactic to make the suspect believe that they were stuck there and couldn't decide to stop talking. Which... That sounds like something you'd get a lawyer for to help explain the situation.