I already told you Haitian Jack and Jimmy Henchman set the thing up with East Coast record labels consent, because they were under extortion and Keefe D and Baby Lane finished the job on the Strip cuz everyone knew DR was en route to 662.
East Coast drug dealers had East Coast record labels under extortion.
The whole of Bad Boy was upstairs. Puff knew, and by extension BIG.
Pac spoke out on Haitian Jack (who was a co defendant in his rape case) in the Daily News and he was set to get robbed for revenge. This might seem an unwarranted response but Jack was a widely feared stick up kid (even Mike Tyson was known to be wary of him), and robbing people was a casual thing for him.
The issue against BIG was that if he knew this was going to happen and didn't warn Pac sufficiently, then by affiliation he was just as bad as the people who did it. Weeks prior to the events of Quads Studios BIG had warned Pac not to hang out with Jack, but failed to mention why. If you've seen the movie notorious there's even a small scene on it.