This combination of undated file photos shows Tamerlan Tsarnaev, 26, left, and Dzhokhar Tsarnaev, 19.
The Boston bombing suspects initially planned to set off their bombs on July 4 before changing their minds and detonating them at the Boston Marathon finish line on Patriot's Day instead, suspect Dzhokhar Tsarnaev told investigators, NBC News reported Thursday.
Sources familiar with the interrogation told NBC News that Tsarnaev, 19, said he and his brother Tamerlan, 26, wound up staging the attack when and where they did because they finished constructing them earlier than they had expected. They built the bombs in Tamerlan's house, officials said he told them.
Those revelations came as investigators pieced together the details of the bombs' construction, with newly acquired evidence providing important clues, and as Tamerlan's body was claimed Thursday.
The Tsarnaev brothers are suspected of setting off the twin pressure cooker bombs that killed three people and wounded hundreds on April 15, as well as of killing a police officer days later. Tamerlan was killed April 18 in a wild shootout with police, and after a city-wide manhunt, Dzhokhar was captured the next day.
New developments in the case came Wednesday, as three of his friends were arrested and charged with obstructing justice and lying to investigators over their removal of some of Tsarnaev's belongings — a backpack containing emptied fireworks and a laptop — from his dorm room following the bombings.
The friends turned the laptop over to the FBI, and investigators tracked down the backpack with its fireworks inside. It had been thrown into a dumpster but was recovered in a nearby landfill.
Thursday night, meanwhile, Massachusetts officials said Tamerlan Tsarnaev's body had been claimed. Department of Public Safety spokesman Terrel Harris told the Associated Press that a funeral home retained by Tsarnaev's family picked up his remains Thursday. He had no more information.
The medical examiner determined Tsarnaev's cause of death Monday, but officials said it wouldn't become public until his remains were released and a death certificate was filed. It was unclear Thursday evening whether the death certificate had been filed.
Tsarnaev's widow, Katherine Russell, who has been living in North Kingstown, R.I., learned this week that the medical examiner was ready to release his body and wanted it released to his side of the family, her attorney Amato DeLuca said days ago.
Tsarnaev's uncle Ruslan Tsarni, of Maryland, said Tuesday night the family would take the body.
"Of course, family members will take possession of the body," Tsarni said. "We'll do it. We will do it. A family is a family."