A spokesman for the prime minister of Pakistan said Wednesday that the office received a letter filled with anthrax last year, the Associated Press reported.
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The letter came from a university professor in October 2011, but it is not clear why the news was only released today, several months later.
The AP reported that Islamabad's police office had only learned of the incident recently, and a criminal case was filed Tuesday. Tests conducted at a Pakistani laboratory confirmed the substance was anthrax. No arrests have been made.
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Reuters said, "The parcel was mailed from the town of Jamshoro in the southern Pakistani province of Sindh."
Al Qaeda, which is active in Pakistan, is known to carry out attacks there with firearms and explosives, but the group has never used biological weapons. A spate of anthrax attacks in the US in 2001 was not connected to Al Qaeda, according to the AP.