Devil's Teardrop — Jeffery Deaver

New Year's Eve, 1999. An early morning machine-gun attack by the Digger, an emotionless, robot-like madman, leaves dozens dead in the Washington, D.C., subway system. In a message to the mayor's office, a criminal mastermind demands twenty million dollars by midnight or the capital will again be at the mercy of his accomplice. But en route to the money drop, the devious extortionist is killed in a freak accident. The Digger, without orders to desist, prepares for his midnight massacre. With the ransom note as the only evidence, Special Agent Margaret Lukas calls upon Parker Kincaid, a retired FBI agent and top forensic document examiner, to join the manhunt. By midnight, they must track down the Digger--or for hundreds, the first moments of the new century will be their last on earth.