Who is Nicky Wilson from The Midnight Club and what is their importance?

Nicky Wilson is a convicted murderer who is in prison. He claims his conviction was the result of the government's need to convict a black man. He also claims he is innocent. When Sarah visits him in jail, she asks about the Midnight Club. Nicky, however, becomes agitated and refuses to speak to her. He later calls Sarah and asks her to return to the prison, where he tells her that the Midnight Club is planning a meeting in Atlantic City. It is this bit of information that is responsible for Stef's arrival in Atlantic City where he will witness the mass killings of the members of the Midnight Club.