ST. LOUIS COUNTY, Mo. — Prosecutors have filed murder charges in Friday’s house explosion near Black Jack that killed a man and three teenagers who were assembling fireworks in a garage. Terrell Cooks, 37, and Seneca Mahan, 43, provided materials to create explosive powder that would be loaded into fireworks canisters at the home at 6680 Parker Road, according to charging documents. Cooks and Mahan are charged with three counts of second-degree murder, two counts of endangering the welfare of a child and two counts of unlawful possession of an illegal weapon. The St. Louis Post-Dispatch first …