American law enforcement officials said Friday that they were trying to determine whether the Pakistani government was involved in a plot by a South African businessman to export trigger devices that could be used for nuclear weapons. “That’s one possibility that we’re investigating,” said one official who spoke on condition of anonymity. “We know these devices went to Pakistan. What we’re still investigating is where exactly they ended up and who was behind it.” Asher Karni, an Israeli who lives in South Africa, was arrested in Denver earlier this month on charges that he had illegally exported the devices to Pakistan without a license. In court documents, the American authorities charge that Mr. Karni, 50, was at the center of a global operation that used front companies and false billing records to route the trigger devices from a private manufacturer in Salem, Mass., to South Africa, the United Arab Emirates and ultimately Pakistan. Full Story