CIUDAD JUAREZ, Mexico — Mexican federal police said Saturday they discovered a basement arsenal hidden behind the mirrors of a home gym that included three anti-aircraft guns, dozens of grenades, a grenade launcher, AK-47s and other high-powered weapons. The neatly ordered stockpile found in an upscale neighborhood in Ciudad Juarez, across the border from El Paso, Texas, also contained several makes of machine guns, rifles, a shotgun and more than 26,000 ammunition cartridges, according to Raul Avila Ibarra, the federal police commissioner in charge of the city. Police say they discovered the weapons Friday while searching a house near the...