WESTLAKE, La. — In the hours before his death on the evening of Dec. 30, the first black mayor of this overwhelmingly white town started learning his new job. About noon, he set City Hall's alarm system for the first time. He got instructions on how to raise and lower the U.S. flag. He had already ordered a new mayoral letterhead with his name on it and a button-down shirt embroidered "Gerald Washington, Mayor." A few hours later he indulged in a hobby, placing a $4 bet at a nearby horse racing track. But by 10 p.m. Gerald "Wash" Washington...