An insurgent blew up his car in a Baghdad square, killing four people in the first significant suicide bombing in the capital in weeks. More than 20 Iraqis died in a swell of violence, including a bomb that killed a police colonel and four children. In Sunday's attack, the bomber plowed his explosives-laden car into two police vehicles in downtown Tahrir Square at 11:30 a.m., killing two police officers and two civilians. U.S. troops rushing to the scene in Humvees found bystanders tending to 11 wounded.