The characteristics of the crime drama include a suspect and an investigator, a murder or a crime, and clues.
And Then There Were None follows the traditional crime drama formula by including an investigator and suspects. There are some twists though. Each person in the group has supposedly committed murder, so each person is a suspect. Also, they do not know who invited them so there is no clear investigator. Each person fulfills that role theoretically. Justice Wargrave eventually turns out to be the investigator AND the culprit! He lured the “murderers” to their deaths in order to get revenge for their supposed crimes.
Wargrave provided a clue when he summed up for the survivors.
"So far, the murderer has had an easy task since his victims have been unsuspicious. From now on, it is our task to suspect each and every one amongst us.” (ch 8, p. 165)
Clues are another important aspect of the mystery genre. The reader is supposed to play along, learning things that will lead to the suspect before the truth is revealed. There are some hints that Wargrave is the killer, including the fact that he took charge. However, this did not clearly lead people to him. He faked his death, which would lead the reader to believe it wasn’t him after all. Then, when his letter was found, the reader realized that he had lured everyone to their deaths to punish them. The clues all begin to make sense when you know the answer!
Most crime fiction and mystery stories do include a “reveal” to tell the reader what really happened. Wargrave revealed his role even after his actual death.