Detecting a form of cheating

[Savaron]

In germany a cheater got detected, who played for years only in the 1/10 seat and crushed the game.

In this casino, cards were counted only on defined times.

He just kept one card and throws the other one in the muck to the rest of the cards. He did it twice and tada, he plays Holdem with 4 cards = huge advantage

Noone noticed it for years, though they watched him carefully. Once, a dealer counted the cards too early, he desperately threw his remaining cards in the muck, and was caught.