Nathan Duarte is a prison guard stationed at Sing Sing and responsible for the transfer and supervision of Dominican inmate Carlos Torres. Torres also figured out somehow Duarte is gay and not only screamed homophobic harassment at him, but Torres' shrieks outed Duarte to his whole division, leading to him needing a transfer of assignment.
When Torres was found brutally raped to death in his cell, Duarte became a suspect. He was horrified and thought he was being targeted off archaic gay hate, but detectives insisted they just knew he was a witness and needed to rule him out. He revealed his alibi was a down-low affair with a man with a wife, attorney Chris Hartford, which is what he clocked out for around the suspected time Torres was murdered.
Hartford was discreetly questioned, and he confirmed the two men met for some alone time. Duarte was affirmatively cleared of suspicion when it was confirmed Torres was raped, before even making it to Sing Sing and died from the injuries after he was put in a cell. (SVU: "Rotten")