Letter found in Rifle written to the Kid

[MissyS]

I found this story interesting and wonder who it was that wrote the letter to Billy from Fort Lyon (more likely) Colorado?  The rifle was found in a deserted village in an adobe near Anton Chico, the rifle was later determined was an 1892 Winchester. I wonder if the letter could have been written from Joseph Antrim who may have been living in Colorado? looking at some of Jesse James writing, I see a little bit of a possible similarity in a few letters.

billythekidshistoricalcoalition.com/a-letter-to-billy-kid/