Police say they have zeroed in on a convicted sex offender as a ?person of interest? in the case of a woman found dead in a salt marsh over Labor Day weekend.According to police, Michael Walsh, 29, was arrested Wednesday on charges unrelated to the discovery of the body of Noel Senerchia. At the time of his arrest, police say detectives tried to ask Walsh questions about Senerchia, who they believe once dated Walsh. Police say Walsh refused to answer. Walsh was arrested for violating an obligation to disclose his address to police every 90 days.Senerchia was found floating in a bag in a Rowayton salt marsh. Autopsy results are not conclusive and her death has not yet been ruled a homicide.