Authorities say the Tsarnaev brothers had planned to drive to New York to explode their remaining bombs last Thursday, but their plans went off track when the owner of the car they carjacked escaped.
The information came from an interrogation of 19-year-old Dzhokhar Tsarnaev, who at first had said their plan was to go to New York to party. He changed his story in a second interview, officials said. The NYPD says the brothers had six improvised explosive devices at their disposal.
Sixteen hours after the interrogation began, Dzhokhar Tsarnaev stopped talking to investigators after a magistrate judge and a representative from the U.S. Attorney's office entered his hospital room and gave him his Miranda warning, according to officials who wished to remain anonymous.
Before he was read his rights, the suspect told authorities that his older brother, 26-year-old Tamerlan Tsarnaev, had recently recruited him to be part of the attack that detonated pressure-cooker bombs at the marathon finish line, officials said. Those April 15 blasts killed three spectators and sent more than 260 people to the hospital.
The FBI searched a landfill in New Bedford, Mass., on Thursday morning, looking for discarded packaging or homemade bombs that may have been used in a test. Overnight, federal agents and police discovered a stash of fireworks -- some which had been emptied of their gunpowder. Officials believe Tamerlan Tsarnaev purchased the fireworks to help make the explosives.
The CIA told the Associated Press that Tamerlan Tsarnaev was named on a terrorist database 18 months ago. This information that he was included within a huge, classified database of known and suspected terrorists before the attacks was expected to drive congressional inquiries in coming weeks about whether the Obama administration adequately investigated tips from Russia that Tsarnaev had posed a security threat.
Dzhokhar Tsarnaev was captured Friday following a massive manhunt that shut down the city of Boston. He was discovered hiding in a boat covered by a tarp, which was parked on the property of a home in nearby Watertown.
Officials said he was unarmed when police captured him hiding in the boat. Authorities originally said they had exchanged gunfire with him but later said no gun was found in the boat.
Tamerlan Tsarnaev was killed in a shootout with police hours earlier. Investigators said they recovered one 9-mm handgun from that scene. His body remains at the medical examiner's office, still unclaimed by next of kin.
The suspects' parents, Anzor Tsarnaev and Zubeidat Tsarnaeva, spoke out at a news conference in Russia on Thursday. The father said he plans to travel to the U.S. Thursday or Friday and wants to take Tamerlan's body back to Russia.
Their mother blasted the press, defending her sons and saying she doubted evidence, photos and video.
However, officials said Dzhokhar told the FBI that he and his brother were angry about the U.S. wars in Afghanistan and Iraq and the killing of Muslims there, officials said. Investigators have said the brothers appeared to have been radicalized through jihadist materials on the Internet.
The Associated Press contributed to this report.