I am not researching the Doerr name, but I came across this article in the Chicago Tribune:
Chicago Tribune, Nov. 17, 1909, page 2.
Conductor Accidentally Killed.
R. J. Doerr, a conductor on the Oak Park elevated railroad, was shot and killed yesterday by his 12 year old brother, Charles Doerr, while the latter was playing with a 22 caliber rifle in their residence, 6121 Honore street. Doerr had warned his brother not to play with the rifle. A moment later the boy caught his sleeve in the trigger guard and the weapon exploded. The older brother, sitting across the room, lurched forward and fell with his arms on a table. The bullet passed directly through his heart.