OK, I’m going to try this once more (and then once more..)
I can’t possibly be saying Lashon Hara (or motzi shem ra, whatever you choose to call it) if I don’t know who I’m talking about. As long as I’m not saying anything derogatory “those people are crazy”, there’s no forbidden speech on saying possible theories why someone did what SOMEONE ELSE said he did. And there’s ABSOLUTELY NOTHING NOT to be mekabel.
The one who knows anything, knows what she knows. She knows the facts. And he’s offering possible reasons. Yes, she’s allowed to believe that Abba_s wrote it. And she’s of course allowed to think along those lines. Is she allowed to take it for certain? a) Why in the world would she? b) What’s the difference to her, she’s moving on in life.
And, in your case too, it’s probably permitted. For the same reasons I stated.
and about your friend’s 14 yr old chiddush – no, your not allowed to think it’s motzi shem ra, because you’re suspecting another Jew. Not being Mekabel means just that. Don’t believe (for certain). Nothing more – noting less. Don’t take it for granted.
(which by rote, these aforementioned cases are ALREADY excluded, as explained)
To sum: There is NO ISSUR on offering theories to the report of another anonymous persons actions, whatsoever.