Did we read the same article?
>Western Union (...) admitted "to aiding and abetting wire fraud" by allowing scammers to process transactions, even when the company realized its agents were helping scammers avoid detection
Furthermore:
>Between 2004 and 2012, the Colorado-based company knew of fraudulent transactions but failed to take steps that would have resulted in disciplining of 2,000 agents, authorities said.
If the prosecutors were able to prove that WU was aware that the transactions were fraudulent your comment makes no sense. They didn't need to be "a quasi-law enforcement agency" because they already knew that the transactions were fraudulent.