OK, ready or not, here is my theory, right or wrong.
I think it all started out as a bungled attempt to get the letters away from Jared, not to kill him intentionally. I don't think I can connect all the dots completely but I think that Alison, the Boyds, the Davis' and the Snyders had it planned out to just steal the letters and keep them hidden for a while if not forever.
Alison would get up when Jared left to go downstairs and search their rooms for the letters. He would have to have at least a copy of them at the Conference. Then Taylor was to go downstairs, got to the bathroom where he had a costume hid and put it on. Yvonne would come downstairs and she would find Jared knocked out in the hallway. With so many Elvis artists around, who could tell one from the other. Max was also supposed to be in costume already. He would be the Elvis that was running away with blood on his suit. Taylor or Max one was supposed to have a knife to brandish at Jared to make it look like a robbery. But as with all good plans that are not completely planned out, things started going wrong very quickly.
Jared was not knocked out and started defending himself, so in the heat of the moment and without thinking, they stabbed him and Jared died. Taylor took his suit off but not his wig hoping he would not be recognized and ran back up stairs. Max had blood on his suit because he checked to see if Jared was still alive and got blood on his hands, which he wiped on his suit. He ran to the bathroom and proceeded to wash his hands. He didn't know Buzz was hiding in the bathroom and that he had seen Rose and Taylor remove their "Elvis skin". Buzz saw the blood in the sink and Max's reflection in the mirror above the sink. He then left with the suit wadded up under his arm. He took the suit to Lyndsey and she washed it. Yvonne came along as scheduled but she didn't know about the knife. She thought Taylor stabbed Jared so she panicked and hid the knife.
Now, although it was not the plan to kill Jared, everybody was in a win-win situation. Alison didn't have to worry about Jared making all that money and leaving her for a younger woman. Before the letters came along, she held the purse strings. If Jared succeeded in his plan to reveal the letters, he would make a lot of money on his own and wouldn't need her anymore. The synders and the conference's reputations were no longer in jeopardy and and would be able to continue to promote more such conferences. Sonya would be put back in as a keynote speaker and wouldn't have to worry about her future as a speaker. Peter would get the letters back for Joy. Taylor would have the last laugh at Jared for ending their partnership and Yvonne would have her own revenge for dumping her the way he did and cutting them out of a lot of money on the letters and the book.
I may have the key players in the wrong position as to who did what, but I think they all conspired together and that Max was the one who actually stabbed Jared. But all in all, if this is the way it went down, they are all guilty.
Now what to you guys think?