He broke the rules and was punished for it but he didn't cheat in the gaining advantage sense. Don't be silly. He was just a retard which is hardly a surprise.
Muralitheran had to have the rules change because he was a chucker. Even with the rules he was a chucker except for brief periods during testing following extensive remedial training. In games he was as bad as ever. Of course after the victimisation of the umpires who called himn meant that nobody was going to risk their career by calling him again.
In almost any other country it wouldn't be an issue because he would have been weeded out as a chucker at the grassroot level.