Captain Fritz's doing what you claim is your imaginary construct, Mr Cakebread, not mine!
Well I'd hoped that you might offer some idea...
I'll admit I can only speculate...But....I seriously believe that ol Cap Fritz was in the early stages of Alzheimers (and that's why he was involved in the conspiracy in the first place)
I believe that the daft Capt Fritz really believed that he could pull a switch-a-roo and present a 7.65 mauser that could be traced to an "Oswald accomplice'.... He knew that there were more shots fired than the carcano was capable of delivering in 6 seconds... Therefore he needed another Scapegoat to assist Oswald in performing the ambush. So Shazam! he found the accomplice's rifle..... And he presented that rifle for Seymour Weitzman's inspection, and description to the FBI.
That little bud never blossomed , because it wasn't necessary after they lynched Lee Oswald....