Dzhokhar Tsarnaev, the surviving suspect in the Boston Marathon bombings, told federal investigators that he and his brother initially planned to detonate explosives at Boston’s vaunted July Fourth celebration on the Charles River Esplanade, according to two officials briefed on the interrogation.
When the brothers built the bombs faster than they had anticipated, they drove around Boston and Cambridge sometime before Patriots Day casing police stations, with an alternative plan to launch an attack on law enforcement officers, one of the officials said.
“They surveyed these police stations, multiple stations in Boston and one in Cambridge,” said the official, who spoke on the condition of anonymity. “They built the bombs so fast that they decided to move the whole plan up.”
The fresh details from the FBI’s interrogation of Dzhokhar Tsarnaev further underscores the notion of an oddly haphazard plot, one that ultimately focused on the home stretch and finish line of the Boston Marathon, the city’s most iconic sporting event.
In other developments Thursday, the lawyer for a Kazakh national charged with trying to destroy evidence in the bombing case said that his client turned over Tsarnaev’s laptop computer to the FBI four days after the deadly explosions.
The computer, which could hold key information about reasons and planning for the bombing, was handed to FBI agents during their first interview with Dias Kadyrbayev, according to his lawyer, Robert G. Stahl.
Kadyrbayev, 19, was charged Wednesday with two other men with trying to destroy or cover up evidence linking Tsarnaev, their friend at the University of Massachusetts Dartmouth, to the April 15 bombing. Tsarnaev’s friends are not implicated in the actual bombing plot.
According to authorities, Kadyrbayev told them he took the laptop and a backpack from Tsarnaev’s dorm room at UMass Dartmouth after seeing Tsarnaev in photos released by the FBI on April 18 during a desperate search for the bombing suspects. Kadyrbayev helped discard the backpack, which held an array of fireworks, in a dumpster outside the New Bedford apartment where he lived, authorities said.
Lawyers for the accused said their clients did not realize Tsarnaev was one of the bombing suspects. But federal investigators said that Tsarnaev recently told Azamat Tazhayakov and Kadyrbayev that he knew how to make a bomb and that Tsarnaev, Tazhayakov, and others had set off fireworks along the Charles River in Boston a couple of months before the bombings.
In Boston on Thursday afternoon, the body of Tamerlan Tsarnaev, Dzhokhar’s brother, was released from the state medical examiner’s office to an uncle, Ruslan Tsarni of Maryland, and Tamerlan’s two sisters, according to a human rights activist in Russia who is helping the family.
Tamerlan Tsarnaev, suspected of the bombing with his brother, died following a shoot-out with police in Watertown on April 19. Dzhokhar, who is believed to have run over Tamerlan with a stolen car as he fled the shoot-out, later escaped on foot before being captured that evening.
Television helicopters followed the hearse they believed was carrying Tsarnaev’s body to the Dyer-Lake Funeral Home and Cremation Services in North Attleborough.
About 30 people gathered across the street from the funeral home about 9:30 p.m. and expressed shock at the arrival of the corpse.
Some onlookers were wrapped in American flags and carried signs.
“I think it’s just atrocious what they’re doing here,” said Garrett Plath, a 20-year-old town resident who held a sign that said, “Justice Is Served Boston Strong.”
State Representative Elizabeth Poirier, a North Attleborough Republican, said police told her they were waiting to hear from a lawyer for the Tsarnaev family on Friday.
“I understand suspect number one is here,” she said. “And I’m very amazed at that.”
Three police cruisers were parked in front of the entrance to the funeral home, and an officer told a reporter that media members were not permitted to approach the building.
Those gathered outside were for the most part orderly, though someone shouted at one point, “Burn his [expletive] body!”
Funeral home managers did not respond to calls for comment on Thursday.
A cause of death for Tsarnaev will be made public once the funeral-service provider files a death certificate, said Terrel Harris, a spokesman for the medical examiner’s office.
Kheda Saratova, the human rights activist, said the Tsarnaev family does not intend to bury Tamerlan until they find an independent coroner to issue a cause of death. The Tsarnaevs have remained dubious of reports that police were taking Tamerlan into custody when Dzhokhar reportedly ran him over.
“The family is afraid that if Tamerlan is buried before they get all the answers, many secrets will be buried with him, and this will make it harder for Dzhokhar to defend himself in court,” Saratova said.
Dzhokhar Tsarnaev is being held at a federal prison hospital in Ayer. The three men charged with obstructing the investigation — Kadyrbayev, Tazhayakov, 19, a Kazakh national; and Robel Phillipos, 19, of Cambridge — are being held at the Essex County Correctional Facility in Middleton.
The bombings killed three people and wounded more than 260 near the Marathon finish line on Boylston Street. Seventeen bombing victims remained hospitalized Thursday, including one child at Boston Children’s Hospital. None is in critical condition, one is listed as serious, and the rest are in fair or good condition.
The government of Kazakhstan said Thursday that its officials are cooperating with US authorities, but that “we would like to emphasize that our citizens did not receive charges of involvement in the organization of Boston Marathon bombings. They were charged with destroying evidence.”
The statement added, “As we have repeatedly stressed, Kazakhstan strongly condemns any form of terrorism.”
Although the two Kazakh students arrested Wednesday are not accused of being part of the bombing plot, questions have arisen about a novelty license plate, “Terrorista #1,” that appeared on the front of the BMW they drove.
Tazhayakov’s father dismissed suggestions that the plate carried any sinister significance.
“Terrorista #1 doesn’t mean Osama bin Laden, doesn’t mean ‘terrorist.’ In their slang, it means happy-go-lucky, a leader of the pack, that sort of thing, and not that they’re going to blow someone up,” Tazhayakov’s father, Amir Ismagulov, told a Kazakh television station recently. “They drove around in that car for four months, and no one arrested them.”
A photo released by authorities when Tazhayakov was arrested Wednesday shows an array of fireworks that allegedly were found in Tsarnaev’s backpack. The fireworks have been cut up, and some emptied of explosives, but pyrotechnic and chemistry experts said it would have been difficult to cannibalize them for their black powder.
“They’re clearly consumer fireworks,” said Julie Heckman, executive director of the American Pyrotechnics Association. “You’re not going to get a lot of powder.”
Federal limits on the amount of explosives in fireworks would have made extracting black powder for the Marathon bombs extremely tedious, time-consuming, and inefficient, Heckman said.
However, black powder from the fireworks could have been used as “a fuse or a starter device rather than the actual explosive device,” according to David Coker, a Boston University chemistry professor. The bombers detonated pressure cookers filled with shrapnel.
In one scenario, Coker said, “you would seal up the pressure cooker, and you probably have wires coming in to ignite that black powder.” Then, he said, the powder would burn “at a high enough temperature to ignite the other, more serious explosive device. It could have easily been a stick of dynamite or something like that.”
The fireworks shown in the photo — the remnants of a “fountain” fireworks, and a 96-shot device for a small aerial display — would have held no more than 200 grams of chemical explosives each, much of which would have been used for color effects, according to Bill Weimer, executive vice president of Phantom Fireworks.
A third device shown in the photo, a stack of several Roman candles, would have been limited to 20 grams each, Heckman said.
By contrast, Weimer said he has been told that the pressure-cooker bombs allegedly used by the Tsarnaevs could have held up to 20 pounds each of black powder and shrapnel.
“For somebody to sit and take these consumer fireworks apart and keep the color composition separate would be incredibly difficult,” Heckman said.
In addition, she said, removing black powder — another word for gunpowder — is dangerous. “You never want to take a firework apart. If they were using sharp metal or knives to cut them open, that could create a spark which could then ignite,” Heckman said.
Weimer has said that Tamerlan Tsarnaev purchased two 24-shell mortar kits from the Phantom Fireworks store in Seabrook, N.H., in February.
The Tsarnaevs would have had to procure much more firepower for their bombs, Weimer said. Combining the black powder from the mortar kits with the three types of fireworks shown in the photo would not have been enough, Weimer said.
“They had to accumulate powder from elsewhere, from additional fireworks, or buying black powder directly,” Weimer said.
Although fireworks cannot be sold to private citizens in Massachusetts, federal law allows the purchase of up to 50 pounds of black powder for personal use, such as firing an antique rifle.
Neither of the Tsarnaevs had been issued a Firearms Identification Card, which Massachusetts residents need to buy black powder in the state.
However, they could have bought the explosive in New Hampshire, where Tamerlan purchased the mortar kits.
As an alternative, they could have produced their own gunpowder. “It’s pretty easy to make,” Coker said.
Travis Andersen, Andrea Estes, Peter Schworm, Milton J. Valencia, and Matt Viser of the Globe staff contributed to this report. Brian MacQuarrie can be reached at macquarrie@ globe.com.