My dear lady, in my experience of ill-doing, Providence leaves the work of conviction and chastisement to us mortals—and the process is often fraught with difficulties. There are no short cuts.

Wargrave responds to Miss Brent’s assertion that Mrs. Rogers’s death must have been an act of God resulting from prior sin. From his vantage point of a judge, Wargrave insists that divine intervention seems unlikely, as humankind has the job of administering justice. Unbeknownst to his listeners, Wargrave secretly means himself as the agent of justice. His observation of the difficulties in the process holds the implication that justice sometimes fails to be served. Wargrave appears to have taken upon himself putting right several injustices from the past.

[I]t explains Soldier Island. There are crimes that cannot be brought home to their perpetrators. Instance the Rogerses.’ Another instance, old Wargrave, who committed his murder strictly within the law…. So in the ordinary way you can’t bring his little crime home to him.

Lombard succinctly spells out why U.N. Owen brought him and the other guests to Soldier Island: Some crimes cannot be punished by law, but they still deserve punishment. Lombard’s theory that the unknown U.N. Owen plans to perform his own acts of justice appears correct save for one detail. When Lombard interprets Wargrave as guilty of murder, by including Wargrave among those to be punished, he overlooks him as the prime suspect. Based on U.N. Owen’s criteria, Judge Wargrave’s “murder” was not in fact a crime, because the man Wargrave helped sentence to death warranted his punishment. If Lombard had known this fact, he might have correctly identified U.N. Owen.

We do know why, more or less. Some fanatic with a bee in his bonnet about justice. He was out to get people who were beyond the reach of the law. He picked ten people—whether they were really guilty or not doesn’t matter—

During the investigation of the murders, Inspector Maine debriefs the Commissioner on what the police know. Maine correctly identifies the murderer as a fanatic about justice. However, the question of whether the ten victims were actually guilty very much did matter to the murderer. Maine may believe that since Wargrave’s crime named on the recording was actually a justified killing, the killer didn’t care whether the victims’ crimes were real. In a turn of dramatic irony, the Commissioner’s momentary realization that Wargrave’s “crime” was not real outs Wargrave himself as the murderer.

To see a wretched criminal squirming in the dock, suffering the tortures of the damned… was to me an exquisite pleasure. Mind you, I took no pleasure in seeing an innocent man there.

Wargrave, the mastermind of the murders, explains himself and his actions on Soldier Island in his note found in the bottle. His thirst for justice had always been combined with a “lust to kill” but only for the guilty. This desire led him to become a judge, where he could make sure the innocent went free and the guilty received their fair punishment. Wargrave’s obsession with the guilty suffering makes him especially susceptible to rage when he realizes how many guilty people are not brought to justice by law. He has judged that everyone on Soldier Island was guilty.

There were, I considered, amongst my guests, varying degrees of guilt. Those whose guilt was the lightest should, I considered, pass out first, and not suffer the prolonged mental strain and fear that the more cold-blooded offenders were to suffer.

Wargrave, mastermind of the murders on Soldier Island, takes his need to deliver justice to a homicidal level. He makes a judgment about each of the “guests” and determines how much they should suffer based on their relative guilt—with the fundamental understanding, however, that all deserve die. Marston suffers least because, as someone without the ability to understand right and wrong, no punishment would really help. The longest wait before death was reserved for those who denied any wrongdoing, at least outwardly: Armstrong, Blore, Lombard, and Vera Claythorne.