Sources said after his capture, suspect Dzhokhar Tsarnaev, 19, told authorities that he and his brother, 26-year-old Tamerlan, altered their plot once they realized they had developed working explosives sooner than expected.
According to Dzhokhar, the bombs were assembled in Tamerlan's apartment. The two decided to change course April 12, just three days before the Boston Marathon.
The brothers are accused of setting off two bombs near the marathon's finish line. The explosions killed three people, including an 8-year-old boy, and injured more than 260 others.
Officials said last week that Dzhokhar has stopped cooperating with investigators. Before that, Dzhokhar reportedly said he and Tamerlan learned how to build bombs online and were not funded or directed by any foreign government or rogue group.
Authorities continue to investigate a trip Tamerlan took to Russia in 2012 where he met with known Islamist militants in Dagestan.
In the meantime, Tamerlan's body was released to a funeral service Thursday. The funeral service may file his death certificate Friday, making his cause of death public information.
Tamerlan's widow, Katherine Russell, wanted her husband's remains released to his side of the family, her attorney Amato DeLuca said. Tamerlan's uncle Ruslan Tsarni, of Maryland, said 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."
Tamerlan was killed in a shootout with police in the days following the bombings, while Dzhokhar was captured the day after the shootout.
Boston police on Wednesday said three additional suspects have been taken into custody in connection to the marathon bombings. All three are believed to be Dzhokhar's college friends.
At this point, it does not look like the three played a direct role in the attacks.
ABC News and the Associated Press contributed to this report.