On Aug. 24, federal agents descended on three factories and the Nashville corporate headquarters of the Gibson Guitar Corp. Accompanied by armored SWAT teams with automatic weapons, agents from the Fish and Wildlife Service swarmed the factories, threatening bewildered luthiers, or guitar craftsman, and other frightened employees. A smaller horde invaded the office of CEO Henry Juszkiewicz, pawing through it all day while an armed man stood in the door to block his way. "I was pretty upset," Mr. Juszkiewicz says now, sitting outside that same office. "But you can only do so much when there's a gun in your...