Official: July Fourth celebration Boston bombers' original target

(CNN) -- It could have been July Fourth. Live on television.

The brothers believed responsible for the bloody Boston Marathon bombings originally planned a suicide attack on the city's massive Independence Day celebration, surviving bombing suspect Dzhokhar Tsarnaev told investigators, a U.S. law enforcement official regularly briefed on the investigation told CNN.

The Fourth of July party draws about 500,000 people and is televised nationally on CBS.

Dzhokhar Tsarnaev told investigators that he and his brother, Tamerlan, chose the Boston Marathon only a day or two before the event, according to the official. They changed their plans because their bombs were ready sooner than they expected, the official said.

Those bombs were built in the small apartment that suspect Tamerlan Tsarnaev shared with his wife and child, Dzhokhar Tsarnaev told investigators, according to that law enforcement official.

Fashioned out of pressure cookers that detonated near the finish line on April 15, the bombs killed three people and wounded more than 260 others. Authorities say they believe the brothers later killed a Massachusetts Institute of Technology police officer.

Tamerlan Tsarnaev died four days after the explosions after a firefight with police. Dzhokhar eluded capture until later April 19 when was found hiding in under a boat tarp in the backyard of a Watertown, Massachusetts, home.

He has been charged with using a weapon of mass destruction and faces the death penalty if convicted.

Authorities expect to file a death certificate Friday, a day after Tamerlan's extended family claimed his body.

A black hearse believed carrying the body drove away with it, according to CNN affiliate WCVB-TV in Boston.

The vehicle was met by protesters at a funeral home in North Attleboro, Massachusetts, The Sun Chronicle newspaper reported. The body was transported to another location hours later, the paper reported, citing a funeral home spokesman.

On Friday, the Worcester, Massachusetts, mayor's office said Tsarnaev's funeral service would be held in that city. It was unclear where he will be buried.

Tsarnaev's uncle Ruslan Tsarni -- who has said his nephews had brought shame on the family and all Chechens -- claimed his body, according to a family spokeswoman.

The family plans an independent autopsy before burying the body in a Massachusetts cemetery, spokeswoman Heda Saratova said.

Dzhokhar Tsarnaev, 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.

Three of his friends have also been charged in connection to the bombing.

Azamat Tazhayakov and Dias Kadyrbayev were charged Wednesday with conspiring to discard potentially incriminating items from Dzhokhar Tsarnaev's dorm room. Robel Phillipos was charged with making false statements to investigators.

The FBI is examining Dzhokhar Tsarnaev's laptop, two federal law enforcement officials told CNN.

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 semiautonomous 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 Tsarnaev 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.

CNN's Susan Candiotti and Marina Carver contributed to this report.