FBI agents found boxes in the house of a man who had earlier confessed to an attempt on U.S. and Georgian presidents at a rally in Georgia's capital in May.
Investigators have erected a tent outside Vladimir Arutyunian's home, on the outskirts of Tbilisi, and appeared to be using special equipment to examine the evidence, according to footage shown by Georgian Rustavi-2 television.
Georgian authorities, working with the FBI, were still searching for a motive in the investigation into the grenade attack.
FBI and Georgian agents were questioning Arutyunian's mother, Angela. She said she had been instructed not to discuss details, but that she planned to visit her son on Tuesday. "I don't know if they will let me in to see him or not," she told reporters.
Bush had been visiting Georgia in an effort to cement relations between the United States and Georgia's new pro-Western leadership. No one was harmed in the May grenade incident, but Arutyunian has been charged with killing a police officer in a shootout during his arrest last week. He was shown on television admitting to throwing the grenade, according to footage broadcast locally Saturday, but authorities have not said yet if they plan to charge him in connection with that incident.
Both Bush and Georgian President Mikhail Saakashvili had been behind a bulletproof barrier addressing a rally of thousands in Tbilisi when the grenade landed about 100 feet (30 meters) away. It did not explode, and investigators later said it apparently had malfunctioned.
Earlier Vladimir Arutyunian was quoted as saying by Pravda.ru: "I’ve thrown a grenade at Bush."
Georgia's Interior Ministry said Friday that Arutyunian was believed to have been a member of a political party that supports the former leader of a region largely outside central government control.