My mom kept a diary. My dad didn't know where it was hidden, but I did. After she died, I read the whole thing.
Sean Figueroa is a library volunteer at Sing Sing and the estranged son of serial killer Wade Crewes. While getting closer to Crewes in prison and teaching him how to read, the two hatched a plan to get Crewes wrongfully exonerated of the murders.
Biography[]
Season 1[]

"My dad's inside, if you want to talk to him."
After another home invasion leading to two more murders in Crewes' style, from mask to gun to staging, Holmes and Gregson arrive at the home of Sean's mother Carla, only to find Sean there to say she died of leukemia five years prior and that his "dad" is inside the house. When they refuse, he walks off, only to commit three more murders at a second evocative home invasion, one victim not part of the intended couple. An ex-con named Victor Nardin is found with the gun, but he's quickly cleared because of his depth perception making him incapable of the long-distance shots in the murders. Knowing Crewes could walk free, especially since Terry D'Amico, the prosecutor, planted evidence to squash his alibi, they go looking for who had access to Crewes, knowing now about an accomplice and the intended scheme of the copycat crimes. They find the library staff sheet and the volunteer group Figuero's employed in, revealing him as the new serial killer.[1]

Figueroa's offer.
Holmes and Bell confronted him, where he confesses he found his mother's diary revealing his true parentage and to get closer to Crewes, not only did he volunteer at the prison, he taught Crewes how to read. When Holmes continues pressing the accusation of him being the new killer, Figueroa has none of it. That is until Holmes incentives with how quickly Crewes would take a sentence reduction deal to name an accomplice, asking if Figuero's freedom and Crewes are really worth that. Figureo caves and confesses in full, even providing the evidence down to the missing shoes taken even from the first spree as souvenirs to keep Crewes in prison for like and land his disowned son in jail as well.[1]