Robert Thatcher is one of Dexter Morgan's many victims. He's identified via a blackboard in the background during a meeting about the Bay Harbor Butcher, with Detective Madison being the one covering his case.
Later on, Agent Frank Lundy unzips his bodybag in The Tent to reveal a pile of bones, telling Debra Morgan, Detective Ramos and Angel Batista that he's a janitor for a school district...with no criminal records.