R v Mentuck is a 2001 criminal case in Canada which led to changes in undercover police procedure and how to interrogate suspects.

Clayton Mentuck, a native lad,[2] was accused of killing a 14 year old teenager, Amanda Cook, in 1996.

[3] In April 1998 lawyers revealed that a tape of Mr. Mentuck's police interrogation had been doctored, causing Mr Justice John A. Menzies of the Court of Queen's Bench of Manitoba to issue the stay.

[4] Said Jonathan Kroft, a lawyer fighting the ban on behalf of The Winnipeg Free Press and Thomson Newspapers Ltd:[4] There is a huge public interest in knowing how government operates vis-à-vis the citizen, If this ban becomes permanent, it will be a permanent impediment from knowing how the police operate.Justice Iacobucci wrote for a unanimous Supreme Court a judgment that supported That is, the operational methods were forthwith subject to disclosure.

A three-pronged analysis introduced here by the court required the consideration of the necessity of the ban in relation to its object of protecting the proper administration of justice.

The Mentuck case has become infamous, as the Mr Big procedure has become viewed by the courts as "ingenious, not insidious".