As a child, Devlin was adopted into a large family, where he had three brothers (also adopted) and two sisters. He grew up in Webster Groves, Missouri. His parents and siblings all live in Missouri. Before his arrest, Devlin worked as a manager for Imo's Pizza and as a part-time funeral home worker at Bopp Chapel in Kirkwood, Missouri. He was living in Kirkwood at the time of his arrest. According to a friend, Devlin had once been outgoing. He had changed "to a much quieter person" after he developed diabetes and had two toes amputated in 2002.
