Legend. But...

In 1933, Humphreys helped Al Capone arrange a fake kidnapping. The "victim" of this crime was to be John "Jake the Barber" Factor, a British con artist wanted in his home country for stock swindling. Factor, a Capone friend, was facing extradition proceedings when Humphreys faked his disappearance. In addition, Humphreys framed Capone rival Roger "Terrible" Touhy with the kidnapping charge. Touhy received a 99 year prison sentence.

Sounds like Capone and the Hump were a couple of rats. They used law enforcement to set up and arrest their rival Touhy. That's ratting to me.