A police officer frisks a man allegedly accused of homicide in San Juan Opico, El Salvador, April 10, 2008, during a police operation. The detained man has an 'M' and and 'S' tattooed on his chest, which means he belongs to the gang named "Mara Salvatrucha", one of the most-feared in Central America.
At 9 o'clock on the evening of April 30, 1994, the door bell rang at 31 Willow Way, Woking, a commuter town near London that epitomizes southern England's suburban landscape. Karen Reed, a 33-year-old geophysicist who analyzed seismic data for a living, was enjoying a glass of white wine with a friend when they heard a man's muffled voice through the window. "Have you ordered a pizza?" Karen opened the door — whereupon the pizza deliverer drew a 0.38 pistol and shot her several times in the head with calm deliberation. The killer then ran back to the car and drove...