thats not the question. the question is conspiracy or not, as you state LHO was the lone shooter, which would be implying that there were NO conspiracy. Or do i get anything wrong what've said? The actual shooter could be anyone, unpossible to prove to this day. Since oct 2017 is scheduled to release the last remaining somewhat held back ~3600 documents, i hope they shed new light on this.
There is no question in my mind, that atleast Roselli was heavily involved in the assassination. He had so much connections and ties to and within the CIA, its nearly impossible to overlook. Iam much less sure about Trafficante - there is nearly nothing which can be resarched on him. Also Giancana, those wiretaps of him discussing the shooting with other outfit guys somehow gives him an Alibi, since he just sounds impressed by LHO shooting skills..
If Marcello was the Mastermind, my current state of mind says yes. CAMTEX and other files strongly imply this, this is no steam blown off. And just Ed Becker didn't believe it proves nothing. Also, he was in numerous documentarys and in those he sounded nothing at all disbeliefing that marcello was kennedys killer.
To Nicoletti, as already mentioned, all of these guys have gaps in exactly those timeperiod (oct/nov-dec) or the entire file is still under lock. Which also says a lot.There is no hard evidence that nicoletti was at this day in dallas, atleast not known to me.

What left is all those mysteries around the body, and nobody is more well-versed about all those cover-ups than douglas horne, staff member of the Assassination Records Review Board in the mid-90's. Here is his complete lecture on the assassination:
https://www.youtube.com/watch?v=svDEw3Jgkw8