who is the killer in and then there were none

The killer in "And Then There Were None" is Justice Lawrence Wargrave. He is a retired judge who orchestrates the entire plan to gather and kill the other guests on the island, each of whom had committed crimes but escaped legal punishment. Wargrave kills them according to a twisted sense of justice and his desire to be executioner, ultimately faking his own death during the events and then confessing the murders in a manuscript found after his death. He is both the mastermind and final murderer in Agatha Christie's novel.