WASHINGTON -- Investigators found no evidence of a shooting after the Washington Navy Yard went on lockdown Thursday when someone reported shots fired in the building where a gunman killed 12 workers two years ago.
D.C. police said a woman called from inside a Navy Yard building to report that she might have heard gunshots about 7:20 a.m.
However, investigators found no sign of a shooting, a gunman or anyone injured.
No arrests were made and no weapons found, officials said.
"At this time there is no evidence of gunshots," Mayor Muriel Bowser said.
"There is no evidence of a shooter, and there is no evidence of any victims today."
A U.S. official who spoke on condition of anonymity said Navy security saw surveillance video of two people jumping the fence in the vicinity of the building a couple of minutes before the first report of gunfire.
Security found no one inside the building, the official said.
Officials do not believe the report was a hoax, D.C. Police Chief Cathy Lanier said.
Investigators interviewed the woman who made the call, Lanier said, and she did exactly as authorities regularly tell people: Report anything you think may be suspicious.
Shortly after the report, a heavy police and fire department presence began blocks away from the Navy Yard, with roads blocked and a helicopter hovering overhead.
The FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives were on the scene.
Gates to the Navy Yard were closed, and all people were advised to shelter in place, said Chatney Auger, spokesman for Naval District Washington.
At a news conference later, officials praised the work of all the responding agencies and called it well-coordinated.
Thousands would have been at the base at the time of the reports, Navy public affairs officer Chris Johnson said outside the Navy Yard, the country's oldest naval installation.
In September 2013, military contractor Aaron Alexis killed 12 civilian workers at the Navy Yard's Building 197 before he was fatally shot by police.
The building has since been renamed the Humphreys Building.
It reopened this year.
When facilities specialist Chris Robertson heard an alarm and loudspeaker instructions about 7:30 a.m., he said his first thought was: "Here we go again."
He said his supervisor called at 7:33 a.m. and told him and his two co-workers to leave.
He also said he hadn't noticed anything unusual Thursday morning.
Information for this article was contributed by Brad Foss and Jessica Gresko of The Associated Press.
A Section on 07/03/2015