"We found human remains, and there is an individual under arrest," Marian T. Ryan, the Middlesex district attorney, said during a brief 6:30 p.m. press conference at Cambridge police headquarters.

Additional remains were discovered later in the day inside an apartment building across the street after authorities began a homicide investigation.

CAMBRIDGE — One person is under arrest after a bag of human remains was discovered outside a Biogen building near Kendall Square Saturday morning, according to the Middlesex district attorney's office.

She said the person under arrest will be arraigned Monday in Cambridge District Court on charges of being an accessory after the crime of assault and battery, and improper disposal of human remains.


The human remains were identified, according to a statement from Ryan's office late Saturday night, but the identification is being withheld until relatives are notified. The suspect's identity had not been disclosed as of late Saturday.

"This continues to be an active investigation," said Ryan in the statement. "Detectives are continuing to gather evidence in order to determine the circumstances which led to this discovery."

Ryan said the duffel bag was found at 7:54 a.m. After reviewing surveillance video, Cambridge police went to the apartment building at 157 Sixth St., where they found the additional remains in a common area.

"We are awaiting results from the medical examiner's office," Ryan said, but authorities believe it the remains "to be one person."

The investigation began after Cambridge police reported a "deceased body in an unattended bag," said State Police spokesman David Procopio. State Police personnel documented and secured evidence, and sent in a K-9 unit at 10:50 a.m.

The biotechnology company's Building Two, at 250 Binney St., was cordoned off with caution tape as investigators examined the duffel bag. Police cruisers lined the street, and a large portion of the area was covered with a green tarp. Police closed off Sixth Street for several hours.


A spokesman for Biogen said the company was referring all inquiries to Cambridge police.

Officers at the scene did not provide any information. Jeremy Warnick, a public information officer for the Cambridge Police Department, referred all questions to the district attorney's office.

A 24-year-old contractor at Biogen said that he first noticed police activity at about 9 a.m., and that by noon, more than 30 police vehicles were surrounding the property.

The contractor, who asked not to be identified, said he was working outside when the police activity attracted his attention. Going over to the scene, he said, he saw a red duffel bag that appeared to contain human remains in the bushes outside the building.

"It's weird," he said. "It's usually a quiet street."

The contractor said, "Whoever dumped it has [nerve] to leave it right there; Biogen has lots of cameras, and the police station is right here," a block away.

Biogen employees at the scene declined to comment, saying company officials asked them not to speak with the media.

After police removed the caution tape across an adjacent footpath, a Cambridge couple walked through with their 1-year-old son.

The woman, who would not give her name, said she was alarmed by the incident, as she walks on the path to work every morning.

"It's very startling," she said. "I am shocked."

Raed Alsemari, a 21-year-old resident of the building, said Saturday afternoon that he had been blocked from reentering for about two hours. He said a friend came by to visit him around noon and when he went downstairs to let her in, police prevented the two of them from going back in.


Alsemari, who was dressed in pajamas, said, "I'd really like to change and get back into my home."

Police continued to stand watch outside the Kendall Crossing apartment complex at Sixth and Binney streets into the evening. The Cambridge force had requested assistance from State Police to "shut down access to an area where they were planning to do a building search related to the investigation," Procopio said.

Around 9 p.m., authorities were still inside the apartment building. The doors were locked and an officer checked with anyone entering if they were residents. All others were turned away.

Residents entering or leaving the building declined to comment.

In the statement released Saturday night from Ryan's office, Cambridge Police Commissioner Robert C. Haas said officers would be going door-to-door addressing any questions or concerns residents had. He also asked the public for any further information that could assist the investigation to contact Cambridge police.

"We're confident that this was not a random act and there is no threat to the public's safety as a suspect has been taken into custody," said Haas.

Jacqueline Tempera can be reached at jacqueline.tempera@globe.com. Follow her on twitter @jacktemp. Jennifer Smith can be reached at jennifer.smith@globe.com.