ATHENS, Greece — Greek investigators examining last week’s assassination attempt on a government minister are unraveling evidence of a network of urban guerrilla groups operating across Greece, Spain and Italy. Europe’s international police agency, Europol, in its 2010 report noted a 43-percent increase over the past two years in what it terms “terrorist” strikes in these three countries. In the latest attack in Greece, the minister for the protection of the citizen, Mihalis Chrysochoidis, was sitting just meters away from a bomb that blew up inside his offices last Thursday, killing his deputy. Despite a drumroll of low-intensity terrorist attacks...