Firefighters spray water on a fire at an apartment building in the 1300 block of Peabody Street in Northwest Washington. (Salwan Georges/The Washington Post)

A body was discovered Sunday morning in the Northwest Washington apartment building that was the scene of a three-alarm fire Saturday, and the investigation turned to the unit where the remains were found.

D.C. Fire Chief Gregory M. Dean said the body of an unidentified man was discovered early Sunday in the top-floor apartment believed to be where the blaze originated. The death investigation has been turned over to D.C. police, officials said.

D.C. police spokeswoman Aquita Brown confirmed police are conducting a death investigation but provided no further details.

Dean said search dogs found no signs that there were additional fatalities.

Meanwhile, fire investigators probed the cause of the fire, which displaced about 200 residents from the 55-unit brick complex in the 1300 block of Peabody Street. Residents jumped from windows of the Rolling Terrace apartment complex, some crawling on their hands and knees to avoid smoke, as the fire blazed through the four-floor building.

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“Firefighters showed up that night — Saturday morning — [and] they had people coming out of the window, they had people in the hallway, they had people throughout the building,” Dean said at a news briefing Sunday. “Their first job was to do the rescue.”

Now, he said, the focus turns to the cause and origin of the fire — but investigators face numerous obstacles: namely, the massive pile of rubble left by the blaze.

“The roof fell down, they’ve got gravel in there, they’ve got a certain amount of tar and everything else, so all that’s gonna have to be cut away,” Dean said. “I know we’re not going to finish this investigation today.”

Officials said one resident and five firefighters were taken to the hospital with injuries that were not believed to be life-threatening.­ The firefighters had been treated and released Sunday, the department said.

The fire began about 3 a.m. Saturday, leaving dense smoke and some flames visible for at least six hours. At least a dozen people were rescued by ladder or evacuated through smoke-filled stairwells and hallways.

With “zero visibility,” Dean said Saturday, firefighters swept the building for remaining occupants at least twice but did not find anyone inside. It wasn’t until Saturday night when officials were interviewing building occupants that they learned someone was still unaccounted for.

The Red Cross set up a shelter nearby to assist residents.

Displaced residents trickling in and out of the shelter Sunday described the fear they felt while escaping their burning home. Many were still coming to terms with what happened.

With the fire alarm blaring and the hallway full of smoke, Angel Marquez threw a table and chair through his first-floor apartment window, shattering it to escape.

He had his 12-year-old son jump out and hang onto a power cable until a neighbor below could grab his feet and pull him to safety. Then Marquez jumped out behind his wife, while neighbors yelled “Fuego!” and screamed for help through the smoke.

“What are we going to do?” Marquez, 39, said Sunday in Spanish. Tears streamed down his face as he spoke about his wife and son. “They are very sad,” he said.

The Red Cross assisted 54 families, for a total of 180 people, in the aftermath of the fire, said Paul Carden, the group’s regional disaster officer. Officials interviewed each resident, provided financial assistance and connected them with relevant agencies.

Julio Guity-Guevara, deputy director of the Mayor’s Office on Latino Affairs, said about 45 people at the shelter were children and 60 to 70 percent of the people were of Latino or African descent and did not speak English as their first language. Officials said the apartment building is considered unsafe and it is unknown when or whether residents will be able to return. There was extensive smoke, fire and heat damage to the upper floors, where the fire broke out, and water damage extended to the basement.

Many of the residents expressed concern about replacing important documents, such as passports and identification cards, which the Latino Affairs office is assisting with, ­Guity-Guevara said.

Arianna Royster, executive vice president of Borger Management, which oversees the apartment building, said her team has been working with city agencies and the Red Cross to ensure the displaced residents receive necessary services.

“It’s a tragic situation, and I’m really sorry that our residents have been displaced,” Royster said. “We’re doing everything we can to make them comfortable during this difficult time.”

About 55 people slept on cots on the gymnasium floor at the shelter Saturday night, while others chose to stay with friends and family members in the area, said Larry Handerhan, chief of staff at the city’s Department of Human Services. Forty-seven displaced families were being relocated to hotels Sunday afternoon, he said.

Thomas Gorfu, 23, said he couldn’t sleep Saturday night. The smoky vision of the firefighters rescuing him and his mother, the smell of burning rubber and the sound of the fire alarm kept replaying in his head.

Sitting outside the shelter in new clothes provided by the Red Cross, Gorfu and his 44-year-old father wondered what’s next for their family, originally from Ethiopia.

“I lost everything,” Gorfu said. “It was scary, so the only thing we tried to do is save ourselves.”

Irene Vanegas, 73, started to cry as she thought about her two parakeets, Mariposa and Muñeco, whom she had to leave behind when firefighters rescued her from her apartment.

She said she awoke to darkness Saturday after her nose started itching and she felt something in her throat. She didn’t have time to grab anything; she lost $800 in cash, her passport, Social Security card and other identification.

“The fog was so intense that I felt like falling,” she said in Spanish. “If they didn’t help us, I would be dead because I couldn’t walk.”

Her friends arrived outside the shelter, hugged her and offered any support they could.

“Thank God I find her today,” said a friend, Miriam Murillo, 47.

Outside the apartment building Sunday, Christopher Ochoa, 23, recounted how he was roused Saturday by his father, who smelled smoke and urged him and his younger siblings to evacuate. Ochoa quickly opened the front door and, seeing smoke seeping in, slammed it shut. He slipped on sandals and a rain jacket and ventured back out, where he noticed a neighbor who uses a walker — an elderly woman in her 90s — struggling to make her way out of the building. Ochoa, who works at an occupational health clinic, assisted her outside.

It was only when he got outside that he saw flames pouring from the upper levels. His family was doing fine Sunday, he said.