After three months of investigating drug trafficking in areas hit by violence and drugs, indictments were unsealed yesterday charging 12 Boston men with the distribution of cocaine and heroin in Roxbury and Dorchester. Five of those suspects were also charged with conducting drug deals within 1,000 feet of parks and schools, according to a statement from the Office of US Attorney Carmen M. Ortiz. Authorities targeted areas that were hard hit by drug dealing and related violence at the Warren Gardens Apartments near Dudley Square, Codman Square, and Uphams Corner in Dorchester. If convicted, the individuals can face up to 20 years in prison. The men also charged with dealing near a park or school could receive sentences of up to 40 years.