In doing research for my family history book, I came across this site which chronicles the deaths in the line of duty of old-time peace officers in the early days of Colorado. This one struck me in particular with its poignancy of mistaken identity and good friends. Just seems like there's good stuff for a song there, and also in a few of the others which can be read at that site. Here it is:

Marshal Joseph Simons
Alamosa Police Department

On the night of September 7, 1897, two men were trying to gain entry into the home of O. P. Brown. Brown chased the men away, but one of them threatened to return and shoot him. A little later, Brown saw a man whom he supposed to be the man who had threatened him, and he fired at the man with a shotgun. This man was not the person who had threatened him; it was Marshal Simons who had come to investigate the disturbance. Simons exonerated Brown before he died, as the two had been friends for years.