Nerves rattled by false reports of U.S. Navy Yard shooter in Washington

By Ian Simpson WASHINGTON (Reuters) - A false alarm about a possible shooter at the U.S. Navy Yard in Washington on Thursday rattled nerves amid heightened security for potential domestic threats ahead of the July Fourth holiday weekend. A report of a possible gunman, which was later determined to be unfounded, touched off an hours-long lockdown starting at about 7:45 a.m. EDT (1145 GMT) at the military facility just a mile south of the U.S. Capitol and three miles from the White House. The Navy Yard was the site of a 2013 shooting that left 12 dead. "An employee thought they heard something of concern, they made a call," said Chief Cathy Lanier of the Metropolitan Police Department of the District of Columbia. The call was placed from inside the NAVSEA Command Building around 7:29 a.m. and was relayed to the city's police force, she said. “We don’t believe that it was a malicious hoax or incident like that,” Lanier said. Police responded with a massive presence, temporarily shutting down more than eight blocks of nearby roads. “When we talk to our residents and visitors who want to celebrate Independence Day in the District of Columbia, it should be very clear to everybody that we take clear and credible threats or calls from our citizens and employees very, very seriously,” Lanier said. The incident shook an already tense public as security measures surrounding the national holiday have been tightened to combat possible domestic attacks tied to ISIS. The Department of Homeland Security and the Federal Bureau of Investigation have issued an alert calling for local authorities and the public to remain vigilant for possible threats over the long weekend. The initial call to authorities reported that shots were heard in the Navy Yard's Building 197, according to multiple reports. That was the scene of the 2013 killings by Aaron Alexis, a former sailor who was working for a government technology contractor at the Navy Yard. Lieutenant Commander Scott Williams, 39, a guided missile engineer, was in the building on Thursday as well as on the day of the 2013 shooting. Since 2013, security has been tightened with more ID checks and random bag searches, he said. He told Reuters that police came to his office at about 7:30 a.m. EDT (1130 GMT) and escorted him and colleagues out. "It was pretty much a mirror image of what happened in 2013," he said. "Here we go again." (Additional reporting by Susan Heavey, Bill Trott and Phil Stewart; Writing by Barbara Goldberg; Editing by Jeffrey Benkoe and David Gregorio)