In The Mystery of Edwin Drood, who killed Edwin Drood?

It's a true mystery.

The Mystery of Edwin Drood was Charles Dickens' fifteenth and final novel. He had completed half the chapters when he had a stroke and died. Dickens left no notes concerning the plot and he didn't talk about it to friends or family.

In the novel, Edwin and Rosa are promised to each other as young children. However, as they reach adulthood, their attachment cools. John Jasper is Edwin's uncle and guardian. He is also Rosa's music tutor and secretly in love with her. Neville Landless, friend of both Edwin and Rosa, gets in a violent row with Edwin over his indifference towards Rosa.

Edwin and Rosa decide to end their relationship and have Rosa's guardian tell Edwin's uncle. Neville and Edwin reconcile before Neville goes on a walking tour. Suddenly Edwin disappears. Neville was first accused, but lacking any evidence he is released...a few more chapters and then the author dies and we never know the ending.

Modern theorists have discussed why John Jasper is the killer (this is the most common perception) or why Neville Landless is the killer. Another popular theory is that Edwin Drood isn't killed, but disappears for a while. But how did Charles Dickens want the novel to end?