Red Herrings are a popular technique among writers of mystery novels, plays, television and film. They are meant to throw the reader off the trail of the killer purposely for a time. In other words, they keep the reader guessing along with the characters.
In this novel, several red herrings are evident. First of all, the idea that an unknown Mr. Owen being presented as a killer fools the reader into thinking someone outside the original party. Later, when only two characters remain, the readers assume that one of them is the killer, until they both show up dead. Finally, the third red herring occurs when Justice Wargrave, the actually killer, is supposedly murdered, eliminating him as a suspect in the minds of the readers.