Belko Royce grew up in the same neighborhood as Stan Larsen, a lost boy type who gravitated to Stan’s natural leadership and, eventually, his loving family. He met Stan Larsen when he was a runner in a crime family. Belko is fiercely loyal to the Larsens and spends most of his time helping Stan with the moving company and being an unofficial uncle to the Larsen kids. Sensing the deep grief Stan is experiencing over Rosie's death, Belko offers to "take care of" Darren Richmond, "like old times." "I don't do that anymore," Stan replies. Belko later informs Stan that Bennet Ahmed is the chief suspect in Rosie's murder, and is present when Stan brutally beats the teacher. Belko becomes a suspect himself when Sarah and Holder learn that he was inside the Larsen apartment when Rosie returned home after the dance. When he learns that police are arresting Darren Richmond for the murder of Rosie Larsen, he shoots Richmond. His murder attempt fails and he is taken into custody. At the police station, he obtains a gun and takes a cop hostage, then fatally shoots himself.
In "I'll Let You Know Know When I Get There", Belko's mom is named Bev and she had him later in life. His father is not in the picture. He still lives with her. He makes his bed every night. According to her, when he was young, he had a cat that peed on his bed every night, which prompted his mom to dump the cat in a dumpster. He also has pictures of the Larsen family on his ceiling. His mother wears inappropriate clothing at 70 years old which distressed Belko. When Linden and Holder interrogate Hello, Belko confesses that he was at the Larsen house when Rosie came home the night she died. He hid and heard Rosie on the phone saying "Adela, I'll come." He is very scared of Mitch knowing that he goes in the house when the Larsen aren't there.