|Knoxville Journal and Tribune - July 25, 1902|
image from the Calvin M. McClung Historical Collection
In 1910 we find a John Singleton who is now 38. He's a city policeman, married with a daughter. Ten years later he's 48 and a city detective.
Chicago's Broad Ax, a black paper, carried the story of his appointment.
|The Broad Ax (Chicago, IL) - April 28, 1917|
image from GenealogyBank.com
I think that John Singleton the policeman/detective was also the John Singleton that ran a baseball team in 1902.