PHILADELPHIA — After hours of sifting through the charred remains of an East Lansdowne, Pennsylvania, home on Thursday, investigators retrieved three sets of human remains and a rifle — the beginnings of their painstaking search for evidence as they worked to piece together what led a resident of the home to shoot two police officers before setting the house ablaze the day before.

It was difficult, “gruesome” work, according to Delaware County District Attorney Jack Stollsteimer. And with frustration, he said that the full scope of what happened inside the ruined home on Wednesday afternoon may never be fully understood.

The excavation work at the fire scene on Thursday was hampered by still-smoldering hot spots and several feet of water in the basement. The flames that engulfed the house destroyed important evidence, authorities said, and in the coming days, investigators may need to rely on dental records and other forensic testing to identify victims.

Law enforcement sources said Thursday that the home on Lewis Avenue was occupied by three generations of the Le family. And one of its residents, Canh Le, 43, has been identified by family members as the person who opened fire at two police officers who went there to investigate a report that he had shot his niece, the sources said.

Le lived at the home on Lewis Avenue with his parents; his younger brother, Xuong Le, 40; Xuong’s wife, Britni McLaughlin Le, 37; and the couple’s three young children, those sources said.

Le’s father, Huong, made the initial 911 call to police after his older son reportedly shot one of Xuong Le’s daughters, the sources said. He then ran to safety with his wife, Chin, as police officers arrived to investigate.

Officials don’t believe that the six others made it out of the home.

“These people’s bodies have been destroyed by fire,” Stollsteimer said, adding that identifying the remains would be a “gruesome, time-consuming task.”

Meanwhile, the officers shot and wounded outside the house, David Schiazza of the Lansdowne Police Department and John Meehan of the East Lansdowne department, continued to improve Thursday. Schiazza, 54, was released from Penn Presbyterian Medical Center in the afternoon after being treated for a gunshot wound to his leg. Meehan, 44, remained at the hospital Thursday, awaiting surgery for a gunshot wound to his left arm.

Officials said it was unclear what prompted the reported shooting that initially led the officers to the Le family’s home.

Investigators believe that Canh Le may have killed his five relatives before firing at the officers from a third-floor attic window. The fire that destroyed the home was likely started by the gunman in that same location, officials said.

Le is also presumed to have died in the home, but it was unclear how, authorities said.

East Lansdowne police had no previous contact with Canh Le, or anyone else in his family, officials said. However, Le was arrested by Pennsylvania State Police in 2006 in Middletown Township, about 12 miles from his home on the Delaware County-Chester County border.

In that case, Le was charged with making terroristic threats, trespassing and disorderly conduct. The most serious charge was later dismissed, and Le agreed to community service for the lesser charges, through a diversionary program. The details of what led to Le’s arrest were not immediately available.

Social media posts show that Xuong Le and his wife had three children, two girls and a boy. Photos showed the family smiling together, celebrating such holidays as Christmas and visiting pumpkin patches in the fall.

A man who said he was related to Le declined to speak Thursday when reached by phone.

“We’re not ready to talk,” he said softly.

Britni McLaughlin Le’s loved ones similarly declined an interview, saying only that they were “praying for good news,” as they left their family home in Lansdowne, just a mile and a half from where the shooting and fire erupted.

On Thursday morning, Le’s parents waited behind yellow police tape as officers towed cars out of the driveway, and as excavation equipment was rolled up to the home.

James Cronmiller, 46, used to live across the street and said he knew the Les well. He moved away in 2010, but in the years he lived across the street, he said, the family was quiet and reserved.

“Never a blemish, police were never called here,” he said. “Nobody knew their business, and they didn’t know anybody else’s.”