Death from a Clear Blue Sky

America is under attack. An unknown foreign power is targeting American citizens in the DC area with small missiles. Six men have been killed so far, all in isolated circumstances. Apparently these terrorists can kill people at will and the government does not yet have any defence against them. The public is unaware of these attacks and it is imperative that they do not find out about them until America has developed effective countermeasures. The government will take any action necessary to contain and quarantine knowledge of these attacks. Failure could lead to global warfare, so no measure is off limits. A limited number of casualties is acceptable. The administration is maintaining deniability so the entire operation is classified at the highest level.