MEXICO CITY—Volunteer searchers in northern Mexico led authorities to a series of grisly finds: 17 bodies or skeletal remains buried in the backyards and patios of houses in a low-income housing development, prosecutors in the northern border state of Sonora said late Sunday. They said the bodies had been stacked in four clandestine burial pits, and said searches would continue Monday at other homes. The prosecutors office said the finds were made over the weekend at abandoned houses in the city of Ciudad Obregon. It said the victims had apparently been killed between six months and a year ago. The state prosecutors’ office said the bodies would be subject to genetic and specialized forensics tests to identify them. Photos posted by the prosecutors’ office showed searchers digging by hand and with a backhoe in the yards, and in some cases under the foundations of the homes. While it is more …