It's a belief that the coins which are put into a dead man's mouth will be used in their next life. When that money is stolen, the dead will get it back and the thieves will face consequences from beyond the grave.

It's a belief that money (coins) which were put into a dead man's mouth will be used by them in their next life. When the dead has been disturbed and the money stolen, the dead will somehow get it back and who ever took this money will have to face the consequences.