A great job done by the researcher. It would have been easy to conclude that at least the Marshall's estranged brother was connected in some way with the gang, and left it at that. Normally, records for a picture taken back then, don't exist anymore. It took the relatives of an old west photographer to not only find value in old records probably stored in an attic somewhere, but then donated them to a university who also saw the historical value in them.
I've spent decades researching my family tree. I have documents that I've gathered like gold, but now that I am in such fragile health I have no one to pass them to. I care about all the lost family I have found and have even written some historical fiction about them. I care about them, but will anyone else? Relatives often throw genealogical information into the trash when the compiler passes away.