The adage “Crime doesn’t pay” applies to Fagin, Monks, and Sikes because all of them paid for their crimes, and none of them were successful. Fagin was hanged for his in the end.
All of these characters suffered by the end of the book. In many ways, their fates teach a moral lesson that crime doesn’t pay. Sikes, the burglar who kills Nancy, is betrayed by his friends and even his dog, and arrested and then hangs himself trying to get away. Monks, Oliver’s half-brother who tries to sell him out, ends up dying in prison in America.
Fagin is the man who took Oliver in, but he did not treat his boys well. He forced them to steal for him, and beat them when they didn’t bring enough in. Even the murderous Bill Sikes tells Fagin he abuses the boys. More interested in squirreling away money than their welfare, Fagin eventually ends up alone.
Fagin is sentenced to death by hanging for his crimes. He realizes that no one sympathizes with him.
But in no one face--not even among the women, of whom there were many there--could he read the faintest sympathy with himself, or any feeling but one of all-absorbing interest that he should be condemned. (ch 51)
Brownlow has Oliver visit Fagin in prison, where he has become a trembling shadow of a man. Asking for the papers that prove Oliver’s birth, Brownlow realizes that he needs to bring Oliver himself. Although he blames Oliver for his predicament, he also tells Oliver where the papers are.
Fagin and his crew end up with nothing, but Oliver, who remains good, gets a noble birth and an inheritance, and people who love him and take care of him.