I knew that Mr Bennet should have interviewed Lydia! It's puzzling that he didn't.
So now we know that Wickham's alibi wasn't valid -- he must have returned early from his trip. Did he plan to steal from the residents of Netherfield while they and their servants were occupied hosting the ball? That would explain the jewelry and cufflink Louisa and Darcy were missing. Was Denny in on it? Or did he simply catch him with the stolen goods and threaten to rat on him if he didn't give him what he stole, resulting in Wickham's sudden attack on Denny?
I think it is more likely that Denny, with Wickham's help, was blackmailing the Hursts and Darcy and that the jewelry was offered as payment for Denny [and Wickham's] silence. Perhaps Wickham went to London to try to sell the jewelry and couldn't resulting in the fatal fight at the ball.
Regardless, if they were co-conspirators, they had a fight at the ball resulting in Denny's death. Wickham left the cufflink at the scene of the crime to frame Darcy. The proof will be when he is caught with the other one in his possession.
Mr. Collins just happened to be in the wrong place at the wrong time -- he must have witnessed the attack or saw Wickham searching Denny's pockets.
So, after killing Denny, Wickham thought he would be able to easily enter Denny's room to retrieve evidence implicating him in the blackmail scheme or to get the book detailing the transactions so he could continue the blackmail operation.
Faking his own death and framing Darcy was clever. It enabled him to disappear with no questions asked about his actions.
How exciting! I just can't wait for the next post and hope it will be early. Please?
PS Until he faked his own death, I almost attributed good intentions to Wickham -- that he was trying to protect Georgianna's reputation by retrieving evidence of the impropriety at Ramsgate from Denny's room. What was I thinking?