A police officer in the city of Stoneham, Massachusetts resigned last year after an investigation concluded he’d taken part in repeated incidents of racism. However, CBS Boston reported Tuesday that the officer, former Sergeant Thomas Heller, for months kept a gig as an instructor at the nearby Lynnfield Police Academy, which is run by the Municipal Police Training Committee. Heller stepped down from the Stoneham Police Department after an independent investigator confirmed many stories about his behavior, including using the “N-word” on “approximately half a dozen occasions” while talking to …