> Yes, RM decided to start internal investigation that lasted a few years, instead immediately contacting police, this is why it lasted so long and were so many victims.

Yes, but the distinction here is not actually as useful here as you might think.

In this situation, Royal Mail _are_ the police (the USPS has its own police too). But Royal Mail are also the prosecutors in court (they have/had prosecutorial power).

They didn't really delay sending it to the police because they never would have. It wasn't a police matter because definitively it was a Royal Mail matter. (The Royal Mail has had the power to investigate and prosecute since before there even were police.)

Edit to add: it is now a "Post Office" matter as well because they are distinct businesses as of 2013, and Post Office Ltd is an ordinary company. But the key period concerns a time when they were one and the same