VACAVILLE, Calif. — State and federal investigators pursued leads Monday in an explosion that wounded an elderly Northern California man when he retrieved a newspaper from his driveway.

Police evacuated the Vacaville neighborhood for hours after the Sunday morning blast as they collected evidence and searched for other possible devices. They found none, but neighbors remained on edge even after they were allowed to return home Sunday afternoon.

The victim, a man in his 80s whom police would not identify, was being treated Monday at University of California Davis Medical Center in Sacramento for injuries to one hand, arm and side. His injuries were considered serious but not life-threatening, and his condition was stable late Sunday.

Police say the blast was an isolated incident, but many details remain unclear or have been kept from the public while the investigation continues. Much of the information that police released was intended to quash false reports about the type of bomb or that multiple devices had been found.

It's not even clear whether initial reports were accurate that the object in the man's driveway was his own Sunday newspaper; Sharon Sanchez, who identified herself as the victim's daughter-in-law, told KGO-TV that she saw a newspaper on his coffee table and that he may have been retrieving another newspaper or some other package.

Police in Vacaville — a city about halfway between the Bay Area and Sacramento — were investigating, with assistance Sunday from the bomb squad from Travis Air Force Base, the California Highway Patrol, the FBI and the Bureau of Alcohol, Tobacco and Firearms.