The shots that rang out at the Navy Yard around 8:15 on Monday morning and sent workers running for cover also sent another group scrambling: the law enforcement officers and city officials who had to determine very quickly where it was safe for people to be. Operating in a haze of confusion and misinformation, the responding agencies initially worked alone, and then increasingly in conjunction with one another, to lock down the danger zone and keep civilians out of harm’s way.

Typically, a city works hard to foster vibrant streets, with people hanging out on the sidewalk, ducking into stores, and walking, biking, or driving to work. The Capitol Riverfront neighborhood around the Navy Yard has succeeded tremendously in turning a once-depressed area into a busy residential and commercial community, with popular outdoor spaces and bustling street life. But as the deadliest event in the District since 1982 unfolded, officials had to work in a flash to reverse that, sending a populated area into lockdown.

The process was quick, it was multifaceted, and, at least at the start, it was chaotic.

As soon as it learned of the shooting, the Metro Transit Police Department sent officers to the scene, which was blocks from the Navy Yard station on the Green Line. They swept through that station and quickly made the decision to close its New Jersey Avenue entrance, the one closer to the shootings. The last time a Metro station entrance had been closed for safety reasons was on Aug. 24, when the Metropolitan Police Department had ordered the 7th Street entrance to the Shaw station shut due to a suspicious package that was soon cleared. This time, the cause for the entrance closure was considerably more threatening.

It would remain closed for just a little more than 15 minutes.

Meanwhile, the Navy was the first responder to the shootings, with its Naval Criminal Investigative Service—a federal law enforcement agency—quickly taking the lead. Within two minutes of receiving a call, officers from MPD arrived on the scene, and within seven minutes, they were inside the building and engaging the shooter. The FBI soon joined, and together with MPD led the Unified Command structure that also included the Park Police, NCIS, D.C. Fire and Emergency Medical Services, and others.

MPD, working through the Unified Command, informed city officials of the security perimeter and cleared people from the streets within it. Mayor Vince Gray then spread the word via a series of tweets, urging residents to “stay clear of the Washington Navy Yard and surrounding area this morning.” The D.C. Homeland Security and Emergency Management Agency sent out an alert, at the instruction of MPD, advising people around the Navy Yard and M Street SE to shelter down until further notice.

Metro Transit Police soon realized that the station entrance that had been closed was not only outside the perimeter MPD set up, but actually farther from the site of the shootings than the cluster of reporters who were starting to gather on the scene. They reopened the entrance, and it remained open for the rest of the day. Trains ran on their normal schedule.

MPD Chief Cathy Lanier consulted with Gray and Deputy Mayor for Public Safety and Justice Paul Quander on whether to place schools on lockdown. Ultimately, eight public schools, eight charter schools, and one administrative building were locked down, some as far away as two miles from the shooting. The lockdown ended at the conclusion of the school day, and parents were able to pick children up as scheduled.

The District Department of Transportation helped MPD close the streets needed for emergency vehicle access to the site of the shootings, including South Capitol Street by M Street and the 11th Street Bridge and adjoining roads and ramps. Lanier made the decision to reopen those streets when she determined that the area was safe again. Interstates 295, 395, and 695 reopened shortly after 4 p.m., while streets around Nationals Park remained closed. DDOT announced just after 6 p.m. that all streets were again open.

Meanwhile, the confusion over safety concerns spilled over to Capitol Hill. Around 3 p.m., the Senate sergeant at arms put Senate facilities into lockdown, prohibiting anyone from entering or exiting for two hours. But the House of Representatives, located closer to the Navy Yard, remained open.

MPD spokeswoman Gwendolyn Crump declined to comment on the decision-making that went into the various closures in the city. But at a press conference on Tuesday, Lanier briefly addressed the issue. “The decision to ask residents and others to shelter in place was a decision we made very carefully,” she said. “It was the right decision.”

And then Lanier summed up the huge number of moving parts that went into the sometimes disorderly effort to clear a populated area of its people. “Locking down a city,” she said, “is not easy.”

Photos by Darrow Montgomery