The sibling comments have an interesting worldview: can't fine management cause it's not their firm, can't fine shareholders cause it's not their fault, its nobody's fault.
Holders of common stock are not involved in the daily operations of the company. Not all ownership involves that level of liability. This is by design.
Apparently you didn't think very hard about that one. If you made the owner of a company criminally liable for any wrong-doing by the company's employees, nobody would risk owning a company. It would be impossible to have an advanced economy with these conditions.
They don't need to police it, they need to give the board etc. the proper incentives to do business legally because they will be hurt financially if the business doesn't. The policing is still done by the government agencies.