contaminated mail at the Brentwood sorting facility. An FBI and DOJ investigation determined the likely culprit of the anthrax attacks to be Bruce Edwards Ivins, a scientist, but he committed suicide in July 2008 before formal charges were filed. During three weeks of October 2002, fear spread among residents of the Washington area during the Beltway Sniper attacks. Ten apparently random victims were killed, with three others wounded, before John Allen Muhammad and Lee Boyd Malvo were arrested on October 24, 2002. In 2003 and 2004, a serial arsonist set over 40 fires, mainly in the District and the close-in Maryland suburbs, with one fire killing an older woman. A local man was arrested in the serial arson case in April 2005 and pleaded guilty. The toxin ricin was found in the mailroom of the White House in November 2003 and in the mailroom of U.S. Senate Majority Leader Bill Frist in February 2004. After the September 11 attacks, security was increased in Washington. Screening devices for biological agents, metal detectors, and vehicle barriers became more commonplace at office buildings as well as government buildings. After the 2004 Madrid train bombings, local authorities decided to test explosives detectors on the vulnerable Washington Metro subway system. When U.S. forces in Pakistan raided a house suspected of being a terrorist hideout, they found information several years old about planned attacks on Washington, D.C., New York City, and Newark, New Jersey. It was directed to intelligence officials. On August 1, 2004, the Secretary of Homeland Security put the city on Orange (High) Alert. A few days later, security checkpoints appeared in and around the Capitol Hill and Foggy Bottom neighborhoods, and fences were erected on monuments once freely accessible, such as the United States Capitol. Tours of the White House were limited to those arranged by members of Congress. Screening devices for biological agents, metal detectors, and vehicle barriers became more common at office buildings as well as government buildings and in transportation facilities. This ultra-tight security was referred to as "Fortress Washington"; many people objected to "walling off Washington" based on information several years old. The vehicle inspections set up around the U.S. Capitol were removed in November 2004. Washington Navy Yard shooting On September 16, 2013, the Washington Navy Yard shooting occurred when lone gunman Aaron Alexis fatally shot twelve people and injured three others in a mass shooting at the