Portland police are reviewing security video to determine who intentionally left a suspicious package in the lobby of 100 Middle St. Monday morning.

The large office building, across the street from the Portland police station, was evacuated after the discovery of the device just before 9 a.m.

Police also closed Middle Street to traffic while they inspected the package, which was ultimately determined not to be dangerous.

Police Chief Michael Sauschuck said the package was left on purpose – not inadvertently.

“I believe it was an intentional act,” he said. He would not elaborate on why police believe that, or whether a note was left with the package. He said the package was suspicious because of “the location, the timing and other information that was found at the scene.”

The incident comes during a period of heightened tensions nationwide following the fatal mass shooting last week in San Bernardino, California, which authorities are investigating as a terrorist attack. The two shooters killed 14 people and wounded 21 others before they were killed in a shootout with police.

Asked to describe the object found at 100 Middle St., Sauschuck said it was a package, not a backpack, though he would not disclose its contents.

Sauschuck said police will analyze the evidence recovered at the scene, presumably for fingerprints and biological matter that might yield DNA.

The building houses the U.S. Attorney’s Office, the Secret Service, the FBI’s Maine office and the law firm Bernstein Shur. Sauschuck would not say whether police believe the package was placed there because of the government offices in the building.

Police plan to review security camera footage from the building to determine who left it.

Police said Monday afternoon they had no new developments to report.

Sauschuck would not say how police determined the package was not dangerous.

On Friday, Boston police responded to a suspicious package outside a Coast Guard facility. A man had left a suitcase alongside a Department of Homeland Security vehicle, then walked quickly away, police said.

Police scanned the suitcase and determined it contained some wire and a battery, then detonated the package. They were able to determine it did not pose a threat. The Boston Regional Intelligence Center obtained an image of the man who left it there from security video, disseminated it to the public through the media and were tipped off that afternoon that the man was in Lawrence, Massachusetts. Police charged James Derepentigny, 50, with planting a hoax device.

The building at 100 Middle St. consists of two towers. Bernstein Shur is located in one. The other includes the U.S. Attorney’s Office and other offices within the Department of Justice. Access to the U.S. Attorney’s Office is guarded by a metal detector and law enforcement but the building lobby itself is not.

Emergency officials reopened Middle Street at 11 a.m. Monday after inspecting the package and determining that it was not explosive.

The Police Department’s Hazardous Devices Unit, which is used to respond to suspicious packages and possible explosive devices, was parked in front of the building, and the Federal Protective Service, which is charged with guarding federal buildings and offices, had two vehicles parked near the scene.

Middle Street was blocked off from traffic from Franklin Street to Pearl Street while police conducted their investigation.