WORCESTER — Thomas Laverty, the local plumber convicted last year of using his business as a front for a large marijuana grow while collecting public assistance, was sentenced to 12 years in federal prison Tuesday. Laverty, 40, was convicted by a federal jury in Worcester last January on allegations he and his father, Charles Laverty, used their Millbury plumbing business, Chuck Laverty & Son, as a front for a huge illegal marijuana grow. Over the course of the trial, jurors heard evidence regarding a sophisticated grow operation the Lavertys set up at a warehouse near Thomas Laverty’s...