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.
What makes one of my favorite novels of all time so compelling and addicting to read, are because of these terms that you mentioned: Red Herrings. As cited in the above answer, a Red Herring is often used in either suspense or mystery novels, to keep the reader guessing and on the edge of their seat. As this novel did for me, the Red Herrings in And Then There Were None, are not only well placed in the book, but they completely throw off the reader: exactly what they are meant to do.
Although there are many in this book, three Red Herrings in this novel would be first, the confusion and suspense of who the murder actually is. In the beginning, we start off with 10 suspects. As they get murdered one by one (remember that they were all brought to the island because of murders they committed), they grow increasingly paranoid of each other and afraid that they will be the next to be murdered. However, in the end, we realize that none of the ten were ever the murderer. That person was actually the man who invited them all: Mr. Owen. This would be the second Red Herring.
The third Red Herring that could be considered, is the admitting of each character to their crime. For instance, Dr. Armstrong reluctantly gave way to the details of his murder, while Blore admits to Lombard about his as well. This revelation of truths throughout the novel is really something that not only catches the reader off guard, but also throws the story in a completely different direction as well.