The skeletal remains of three women have been found in or near a Washington, D.C. apartment building under renovation, officials said.

The remains of one woman were discovered inside a crawl space and the other two were in a shallow grave nearby.

The first woman was discovered by construction workers digging in the lower level of a three-story brick apartment building in Congress Heights in southeast Washington last Wednesday.

The workers took photos that showed a skull and other bones they found in the building’s crawl space. There were no personal effects or clothing with the remains, Fox 5 DC reported.

Adan Escobar, one of the construction workers who found the remains, said they first thought the bones were from an animal, until someone spotted the skull and jawbone.

“But when he saw the skull and the jaw, he figured it was a person,” he said, according to the Washington Post.

After police were notified, investigators searched the rest of the building and a nearby wooded area. Cadaver dogs found two additional sets of remains – both female – on Saturday in a shallow grave.

D.C. Police Chief Peter Newsham told reporters on Monday that the two sets of human remains in the wooded area are suspicious and homicide detectives are involved with the investigation.

He said the bones appear to be “very dated,” the Washington Post reported.

LaShon Beamon, communications director for the district’s Office of the Chief Medical Examiner, told reporters the medical examiner will try to identify the remains, their ages and causes of death.

The chief medical examiner told reporters that the victims have likely been dead for more than a year. He said he office was able to determine 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.”

On Monday, police and forensic investigators continued to search for any other possible remains.

The Associated Press contributed to this report.