Bystanders watch as DC firefighters try to extinguish a house fire on Isherwood St. NE, that took place after the home exploded on June 4, 2014 in Washington, D.C. Several of the row houses on the block were damaged from the blast. (Ricky Carioti/The Washington Post)

Maria Christofi Georges visited what was left of her brother’s Northeast Washington home, which exploded, burned and collapsed Wednesday afternoon. There is a man’s body entombed in the rubble, and Georges said Thursday that D.C. police told her it is likely the body of her brother.

Chris J. Christofi, 46, is the only occupant still missing from the four-unit condominium building on Isherwood Street. His prized BMW is parked in the back. Neighbors saw him go inside his home after returning from work early and taking his pit bull, Bella, for a walk.

A short time later, about 3:45 p.m., the explosion shook the eastern edge of Capitol Hill, and one neighbor said she saw Christofi and Bella in the doorway, in flames, before the building crashed on top of them in what became a two-alarm fire.

“We shouted to them to come out. Screams filled the house, but when the upper floor collapsed, everything went quiet,” said Tarsha Devoe, 41, who lives nearby and described an explosion so powerful it shook the ground. “It was like a bomb. It was just one big ‘boom,’ and flames just jumped straight to the roof.”

The cause of the fire remains undetermined, and investigators said that what is left of the building is too dangerous to enter until large pieces are removed. The Bureau of Alcohol, Tobacco, Firearms and Explosives is calling in its elite arson unit to help police and fire officials.

Chris J. Christofi is the only person who has not yet been located after a Capitol Hill condominium burned and collapsed Wednesday, according to his sister, Maria Christofi Georges. (Courtesy of Venn Strategies)

All four apartments in the building are fed by electricity, said Ruben E. Rodriguez, a spokesman for Washington Gas. But he said that on May 19, someone told crews in the area that the smell of gas was coming from the rowhouse adjoining the building where Christofi lived. Rodriguez said that repairs were made and that workers returned the next day to replace the meter. He added that gas crews are working with authorities but had not been given access to the site.

Police said they would not release the victim’s name until the body is recovered and a positive identification made. But Georges is already mourning. She said she’s been told that the body might not be recovered until at least Friday. “The only thing I know is that police let me know it’s likely my brother,” said Georges, who lives in Fairfax County.

Christofi worked at a nonprofit group for 10 years and had just started a job as office manager of a downtown Washington governmental affairs and lobbying firm.

“He is a kind and gentle soul,” said Stephanie E. Silverman, who runs Venn Strategies, which hired Christofi a little more than a year ago. She described him as a “very private person” who “was sweet and kind to a fault.”

He loved his dog, took in stray cats and was a BMW enthusiast. Although he didn’t talk about his own life, those who worked for him said he made sure that his employees were satisfied. “He sometimes went around the office rules to make sure we came first,” said Dan Spagiare, the office manager at PACT Inc., a nonprofit that helps set up projects in developing countries and where Christofi worked before joining Venn.

Christofi, his parents and other relatives moved to Northern Virginia from Cyprus in 1976 after Turkey invaded. Georges said that her brother moved to the District in 2005. “He hated the suburbs and wanted to be a part of the city,” she said. The siblings’ parents are deceased, and the eldest son died a month ago. Other brothers live in Lorton, Cyprus and Australia.

Authorities on Thursday allowed Georges to go past the police tape and get close to where her brother lived. Tearful neighbors described his life on the block, and his final hours at home.

“I just want to know what happened,” Georges said.