Police personnel search a property along Wayne Place SE on Monday after remains were found last week. (Matt McClain/The Washington Post)

Authorities investigating the skeletal remains of three women found last week in Southeast Washington said Monday that the bones of two of the women were commingled in a shallow grave behind an apartment building.

The other set of remains was found under a crawl space in the basement of the same building in the 100 block of Wayne Place SE, in the Congress Heights neighborhood.

D.C. police and the medical examiner warned it could take some time to identify the remains and say how and when the women died. In addition to forensic work, detectives are scouring through missing persons reports, reaching out to current and past tenants of the apartment building and learning the property’s history.

Police Chief Peter Newsham said the bones appear to be “very dated.” He said he appreciates that the situation is disconcerting to residents. “We want to get the answers as quickly as we can.”

Roger Mitchell Jr., the District’s chief medical examiner, said his team is working to clean and examine all the bones, and to separate those found in the grave. He said his office quickly determined all three were female by looking at the pelvis.

“The cause and manner of death is still outstanding,” Mitchell said. “We are still looking for injury and disease.” He said he is confident that DNA can be extracted from the remains to try to make a match.

Remains were found last week on a property along Wayne Place SE. (Adan Escobar/Courtesy Photo)

The first remains were found by contractors Wednesday in the basement under the first floor of the three-story red brick apartment building. Police then used dogs from D.C. Fire and Emergency Medical Services and Fairfax County to search the area and the dogs alerted about 30 yards behind the house in woods that run along Mississippi Avenue. Authorities searched that spot and reported Saturday finding the remains of the two additional women.

Adan Escobar was among the construction workers who saw the bones in the building. He said members of his crew were enlarging the crawl space and digging deeper into the basement floor to make room for additional apartments.

He said the crew had dug about 10 inches into the ground when someone spotted what appeared to be bones of a hand, a skull and a jawbone. “He was thinking it was animals,” Escobar said. “But when he saw the skull and jaw, he figured out it was a person.”

Escobar, 42, of Forestville, Md., said he raced over to the find and called police. “There were no clothes, no hair, no weapons,” Escobar said. “Nothing but bones.”

The apartment building is one of several similar-looking buildings lining both sides of Wayne Place. The one where the remains were found is divided into six apartments for a total of 4,350 square feet. The lot that extends back and into woods, where the other sets of remains were buried, is nearly 8,000 square feet. It was built in 1948, according to Redfin, the real estate website.

Police investigate an apartment house in Southeast Washington after remains were found last week. (Matt McClain/The Washington Post)

The discovery of the remains and 24-hour presence of police officers, forensic scientists from the medical examiner’s office and other law enforcement officials has unnerved residents of this residential neighborhood a half-mile from the Anacostia Freeway. The woods had been a playground for children and the wide alleys that cut through the area a place to park and mingle.

Over the weekend, residents complained that “nobody knows what’s going on,” and the woman who lives in the apartment above where the skull was located called it “creepy” and said she wanted to move.

Newsham would not estimate when his detectives and forensic scientists would conclude their investigation at the site. “We’re going to stay here for as long as it takes,” he said.