Federal authorities were at the apartment of deceased bombing suspect Tamerlan Tsarnaev on Sunday, executing a search warrant, an FBI spokeswoman said.
Amanda Cox said, "There is court-authorized law enforcement activity" at the home in Cambridge, Massachusetts, that Tsarnaev shared with his wife and young daughter.
Workers in white hazmat suits were at the apartment, CNN affiliate WCVB reported.
On Friday, a source briefed on the investigation said investigators found explosives residue in the small apartment.
It has turned up in at least three places, the source said: the kitchen table, the kitchen sink and the bathtub.
Tsarnaev's younger brother, Dzhokhar Tsarnaev, has said they built the bombs there, U.S. law enforcement officials briefed on the progress of the investigation said.
On Sunday, Tamerlan Tsarnaev's body remained at a funeral home, where his uncle said he was trying to deal with the logistics of readying the body for burial.
"I'm here to prepare his body, to wash it, shroud it, to prepare his body," Ruslan Tsarni said.
Tsarni said he was the only family member at the funeral home and had not had contact with Katherine Russell, Tamerlan's widow.
The funeral home owner, Peter Stefan, said he still has yet to find a cemetery willing to accept the body for burial.
A day earlier, he had said that if no gravesite is found, he plans to ask the government to find a grave.
Three cemeteries that Stefan contacted said they feared reprisals, but the funeral home owner said you can't pick and choose when it comes to a burial.
"This is what we do in a civilized society, regardless of the circumstances," Stefan said. "As I told some of them, at the immediate moment, you may fear (reprisal), but later on, when things calm down, people are going to resent you because you didn't do it."
Tsarnaev's death certificate has yet to be filed with the Boston city clerk, and there is no burial plot, according to the funeral home.
Tsarnaev died April 19 after he and his brother, Dzhokhar Tsarnaev, shot a university police officer to death, carjacked an SUV and hurled bombs at officers pursuing them, according to authorities.
A few days earlier -- April 15 -- he and his younger brother allegedly bombed the Boston Marathon, killing three and wounding more than 260.
CNN obtained a copy of Tamerlan Tsarnaev's death certificate, which lists the cause of death as "gunshot wounds of torso and extremities" and "blunt trauma to head and torso."
The document notes that Tsarnaev was shot by police and run over and dragged by a car. It lists the manner of death as homicide and notes that he was "DOA," or dead on arrival.
Authorities have said his younger brother may have run him over as they resisted arrest days after the marathon attacks.
Separately, 12 people remained hospitalized with bombing-related injuries on Saturday, according to a count by CNN. None was in serious condition.
Also, the frantic manhunt more than two weeks ago for the surviving bombing suspect drew the attention of gun rights advocates at their convention in Houston.
National Rifle Association Executive Vice President Wayne LaPierre said residents were "imprisoned" in their homes with no means to protect themselves while police searched for the younger Tsarnaev.
"How many Bostonians wished they had a gun two weeks ago?" he asked.
"Boston proves it. When brave law enforcement officers did their job in that city so courageously, good guys with guns stopped terrorists with guns," he said.
'Everyone deserves to be buried'
Tamerlan Tsarnaev's body remained unclaimed until Thursday, when Tsarni, who had previously publicly condemned his alleged attacks, had a funeral parlor pick up the body.
Tsarni had decried the bomb suspects as "losers" after the attacks.
Their parents in Dagestan have said they will not fly his body back to Russia for burial, spokeswoman Heda Saratova said.
WCVB reported that the hearse that picked up Tsarnaev's body ferried it to a funeral home 30 miles from Boston, near the Rhode Island state line.
Residents of North Attleboro, Massachusetts, took to the streets to boo Tsarnaev when they heard about the presence of the corpse in their town, The Sun Chronicle reported.
Others took to social media to vent anger at the funeral home for accepting the body. It was later transported to Stefan's funeral home, Graham Putnam & Mahoney Funeral Parlors in Worcester.
"Everyone deserves to be buried," he said.
The marathon bombings
Authorities say the brothers carried out the Boston Marathon bombings using explosive devices made with pressure cookers.
Dzhokhar Tsarnaev, 19, is being held at a federal Bureau of Prisons medical facility in Devens, Massachusetts, charged with using a weapon of mass destruction, which carries the death penalty.
He is being treated for gunshot wounds to the head, neck, legs and hands that he received in the shootout with police that led to his brother's
Other target, possible cover-up
The marathon was not the original target, the law enforcement officials said. The brothers had set their sights on a suicide attack on the city's massive Independence Day celebration, which draws about 500,000 people and is televised nationally.
But the bombs were ready sooner than anticipated, and a day or two before the Boston Marathon, they changed their plans, the officials said.
They spoke on the condition that their names not be used because they were not authorized to discuss the matter with the media.
One key question involves whether intelligence, law enforcement and homeland security agencies could have done more in their investigation of Tamerlan Tsarnaev in recent years before the attack and whether they shared information effectively enough. An independent government review is under way.
In an interview with Univision published on its website on Saturday, President Barack Obama said that cooperation among agencies can always get better. But he again defended U.S. efforts.
"I think we can continue to improve and refine how we're engaging and countering terrorist activity," Obama said. "I don't think it's fair to say though that law enforcement dropped the ball."
It is very difficult to prevent attacks when dealing with individuals who are self-radicalized and not part of a massive conspiracy or network, he said about the current belief of investigators looking at the origins of the Boston bombing.
Tamerlan's widow; Dzhokhar's friends
Tamerlan Tsarnaev's widow, Russell, has remained largely out of view since her husband's death, staying in her parents' Rhode Island home.
Her attorney, Amato DeLuca, says the 24-year-old knew nothing about plans to bomb the race, and reports of her husband's involvement came as an "absolute shock" to Russell and her family.
Three of Dzhokhar Tsarnaev's friends have been accused of covering for the bombing suspects.
Azamat Tazhayakov and Dias Kadyrbayev, both from Kazakhstan, were charged Wednesday with conspiring to discard potentially incriminating items from Dzhokhar Tsarnaev's dorm room. Robel Phillipos, a U.S. citizen, was charged with making false statements to investigators.
All three are accused of removing items from Tsarnaev's dorm room after the bombings. According to FBI affidavits released this week, they left with the backpack and Vaseline -- which Tazhayakov believed could be used to make bombs -- and Tsarnaev's laptop.
Investigators found the backpack, fireworks and Vaseline in a landfill last week after a two-day search.
The laptop was turned over by Kadyrbayev on April 19, the same day the FBI raided the apartment he shared with Tazhayakov, Kadyrbayev's attorney Robert Stahl said.
The FBI is examining the laptop, two federal law enforcement officials told CNN.
Authorities have said they believe the Tsarnaev brothers acted alone but are investigating whether they could have learned from or been aided by terror groups, including groups overseas.