Wilson tells them that some weeks before, his young assistant, Vincent Spaulding, urged him to respond to a newspaper want-ad offering highly-paid work to only red-headed male applicants.
With the case solved, he calls Police Inspector Jones and Mr. Merryweather, a director of the bank located next door.
They are John Clay, the Eton- and Oxford-educated grandson of a Royal Duke, considered by Holmes to be the fourth-smartest man in London, who has a long history of criminal activity and his helper Archie.
Under the aliases of Spaulding and Ross, they had contrived the 'Red-Headed League' rigmarole to keep Wilson out of his shop while they dug in the basement, in order to break into the bank vault next door.
Although paying Jabez Wilson four pounds a week was expensive, it was a pittance compared to the ill-gotten thousands they were looking to steal from the bank.