(CNN) -- The bombs used in the Boston Marathon attack were built in the apartment that suspect Tamerlan Tsarnaev shared with his wife and child, a U.S. law enforcement official with first-hand knowledge of the investigation told CNN on Thursday. The official was not authorized to release the information.
Katherine Russell, Tsarnaev's widow, has remained largely out of view inside her parents' North Kingstown home since her husband's death.
It remains unclear what, if anything, Tamerlan's widow might have known or suspected, the source added.
According to her attorney, Amato DeLuca, the 24-year-old widow knew nothing of plans to bomb the race, and reports of her husband's involvement came as an "absolute shock" to Russell and her family.
Tsarnaev and his younger brother, Dzhokhar, initially planned to carry out a suicide-bomb attack on July 4, a U.S. law enforcement official regularly briefed on the Boston bombing investigation told CNN. The source said Dzhokhar Tsarnaev told investigators their bombs were ready earlier than they expected and they decided to move up the date.
Dzhokhar Tsarnaev told investigators that the Boston Marathon was chosen as a target only a day or two before the event, the source said.
It is unclear which specific event would have been targeted but one of the biggest July Fourth celebrations in the country is held in Boston. The annual Boston Pops Fireworks Spectacular hosts 500,000 spectators, according to the event's website. It is televised live nationally on CBS.
The revelation comes the same day the body of Tamerlan Tsarnaev was claimed by his family and later was picked up by a funeral home, according to Terrel Harris, spokesman for the Massachusetts office of the chief medical examiner.
Harris declined to say which funeral home picked it up.
Tsarnaev's cause of death will not be released until the death certificate is filed with the Boston city clerk, he said. The earliest that's expected to happen is Friday morning, Harris said.
His parents in Dagestan will not bring the bombing suspect's body back to Russia and will not bury him until an "independent" autopsy is conducted, family spokeswoman Kheda Saratova said Friday.
One item that may yield some clues into the bombings case is now in the hands of federal officials.
The FBI has a laptop belonging to Dzhokhar Tsarnaev, Tamerlan's younger brother, two federal law enforcement officials told CNN.
The computer was turned over to investigators by one of his friends accused of obstructing justice.
A lawyer for Dias Kadyrbayev tells CNN that his client "turned over the laptop to the FBI." He didn't say when the laptop was turned over.
A law enforcement source confirmed the attorney's account.
Three people died and more than 260 were wounded when two explosive devices fashioned from pressure cookers and other materials exploded in separate locations near the finish line of the Boston Marathon on April 15.
Four people have been charged in connection with the bombing, including Dzhokhar Tsarnaev, who is accused of carrying out the attack along with his brother, Tamerlan, 26. The older brother died April 19 after a firefight with police, hours after authorities released images of the suspected bombers.
Azamat Tazhayakov and Kadyrbayev were charged Wednesday with conspiring to discard potentially incriminating items from Dzhokhar's dorm room, including empty fireworks containers, while Robel Phillipos was charged with making false statements to investigators.
The Kazakhstan Foreign Ministry said Thursday it was offering consular services to Kadyrbayev and Tazhayakov, who are citizens of that country and are in the United States on student visas.
"We would like to emphasize that our citizens did not receive charges of involvement in the organization of the Boston Marathon bombings. They were charged with destroying evidence," the ministry said in a statement.
Dzhokhar, who suffered gunshot wounds to the head, neck, legs and hands, is being held at a federal Bureau of Prisons medical facility in Devens, Massachusetts. He has been charged with using a weapon of mass destruction and could face the death penalty if convicted.
Authorities have said they believe the brothers acted alone, but are investigating whether they could have learned from or been aided by terror groups, including groups overseas.
Of particular interest has been Tamerlan Tsarnaev's 2012 trip to the semi-autonomous Russian republic of Dagestan, home to numerous Islamic militant groups that have warred against Moscow's rule.
Russian authorities asked U.S. officials to investigate Tamerlan some months before the trip, saying they believed he was becoming increasingly involved with radical Islam. The FBI investigated, but found no evidence of extremist activity and closed the case.
U.S. officials learned after the bombings that Russian officials had intercepted a 2011 phone call between the suspect's mother, living in Dagestan, and one of her sons in which they reportedly had a vague conversation about jihad, a law enforcement official told CNN earlier.
Some lawmakers, particularly Republicans, have been critical of how law enforcement officials, intelligence agencies and the administration of President Barack Obama handled the Russian tip.
While Tamerlan Tsarnaev and his mother were added to a terror database following the FBI investigation, Tamerlan was allowed to make his Russian trip in 2012 and return six months later.
CNN's Susan Candiotti and Marina Carver contributed to this report.