WASHINGTON — A former Navy reservist killed at least 12 people on Monday in a mass shooting at a secure military facility that led the authorities to lock down part of the nation’s capital — even after the gunman was killed — in a hunt for two other armed men spotted by video cameras, officials said. 
 
 But by Monday evening, the federal authorities said they believed the shooting was the act of a lone gunman, identified as Aaron Alexis, 34, who was working for a military subcontractor. 
 
 The chaos at the facility, the Washington Navy Yard, started just after 8 a.m. Civilian employees described a scene of confusion as shots erupted through the hallways of the Naval Sea Systems Command headquarters, on the banks of the Anacostia River a few miles from the White House and about a half-mile from the Capitol. 
 
 “I heard three gunshots, pow, pow, pow, straight in a row,” said Patricia Ward, a logistics management specialist from Woodbridge, Va., who was in the cafeteria on the first floor when the shooting started. “About three seconds later, there were four more gunshots, and all of the people in the cafeteria were panicking, trying to figure out which way we were going to run out.” 
 
 Police officers who swarmed the military facility exchanged fire with Mr. Alexis, 34, a former naval reservist in Fort Worth. Police officers shot Mr. Alexis to death, law enforcement officials said, but not before a dozen people were killed and several others, including a city police officer, were wounded and taken to local hospitals. 
 
 Officials said Mr. Alexis drove a rental car to the base and entered using his access as a contractor and shot an officer and one other person outside Building 197, the Sea Systems Command headquarters. Inside, Mr. Alexis made his way to a floor overlooking an atrium and took aim at employees eating breakfast below. 
 
 “He was shooting down from above the people,” one law enforcement official said. “That is where he does most of his damage.” 
 
 The names of seven of the victims were released late Monday: Michael Arnold, 59; Sylvia Frasier, 53; Kathy Gaarde, 62; John Roger Johnson, 73; Frank Kohler, 50; Kenneth Bernard Proctor, 46; and Vishnu Pandit, 61. Officials said names of the other victims would be released after their families had been contacted. All of the victims were believed to be civilians or contractors. No active duty military personnel were killed, said Chief Cathy L. Lanier of Washington. 
 
 One victim was shot in the left temple and was pronounced dead within a minute of arriving at George Washington University Hospital. “This injury was not survivable by any stretch,” a hospital official told reporters. “The patient was dead on the way to the hospital.” 
 
 Eight people were injured. Three of them were shot, including Officer Scott Williams of the Washington police. The others suffered injuries from falls or complained of chest pains. Officer Williams, who served in the canine unit, underwent several hours of surgery for gunshot wounds to his legs. A second victim suffered a gunshot wound to her shoulder. A bullet grazed a third victim’s head but did not penetrate her skull, according to doctors at MedStar Washington Hospital Center. 
 
 Three weapons were found on Mr. Alexis: an AR-15 assault rifle, a shotgun and a semiautomatic pistol, a senior law enforcement officer said. It was unclear whether he had brought all the guns with him, another law enforcement official said, or if he had taken one or more of them from his victims. 
 
 Officials said they were still searching for a motive as they asked the public for help by posting pictures of Mr. Alexis on the F.B.I. Web site. The agency is treating the shooting as a criminal investigation, not one related to terrorism. 
 
 Navy officials said late Monday that Mr. Alexis had worked as a contractor in information technology. A spokesman for Hewlett-Packard said Mr. Alexis had been an employee of a company called The Experts, a subcontractor on an HP Enterprise Services contract. 
 
 Reporting was contributed by Abby Goodnough, Emmarie Huetteman, Thom Shanker, Sarah Maslin Nir and Joseph Goldstein from Washington, and William K. Rashbaum from New York. ||||| A far worse sight lay just ahead. Jirus went to an alley where he thought he would be safe, and talked briefly with a man there about what was going on. Jirus said he heard two gunshots, loudly echoing off the building. It caused him to spin around to look for the source of the noise. But when he turned back, he looked down and saw the man he had been conversing with lying on the ground, shot in the head. 
 
 Uncertain where the shooter was, he ran. 
 
 “I was just lucky,” he said. “The other person was shorter than me. There were two shots, he got that guy, he didn’t get me. . . . The randomness of it — standing right next to me, one person gets shot.” 
 
 At least two police officers were among those shot. Lanier said the D.C. officer worked in the K-9 unit and has been on the force 23 years. She said she has known and worked closely with him for "many, many years." 
 
 "He's got a stellar record," she said. 
 
 "He's got a pretty serious injury, but right now his family is here with him and he's in good spirits," Lanier added. "He's just very grateful for all the other responders who helped get him out of that building and get the medical attention he needed." 
 
 The other was said to be a base officer. Earlier in the say officials at MedStar Washington Hospital Center said his chances for survival were good. 
 
 Janis Orlowski, the chief medical officer at Washington Hospital Center, said three victims in all were brought to the center, all in critical condition but alert, responsive and able to talk with doctors. The victims were also able to speak briefly to law enforcement officers before undergoing surgery or treatment, she said. 
 
 The other two victims at the hospital were female civilians, Orlowski said at a news conference. All are likely to survive. 
 
 The impact of the incident rippled across town, forces schools, offices and homes into an enforced lockdown. 
 
 Senate buildings on Capitol Hill went on lockdown at about 3 p.m., with no one allowed to enter or leave the building, though it was partially lifted toward the end of the day to allow staffers to go home. 
 
 The Nationals, whose ballpark is near the Navy Yard, postponed a Monday night game. Instead, they will play a double header Tuesday at 1 p.m. and 7 p.m. 
 
 Ten public and charter schools and a public school administration building in the District went on lockdown, and flights out of Reagan National Airport were briefly halted, causing delays even after they began departing again. 
 
 Adm. Jonathan W. Greenert, the chief of Naval Operations, was evacuated from his residence at the Navy Yard complex shortly after the first report of shots fired, Navy officials said. 
 
 Greenert, a four-star admiral and member of the Joint Chiefs of Staff, was safely evacuated to the Pentagon along with his wife, Darleen, said Cmdr. Ryan Perry, a Navy spokesman. ||||| These crawls are part of an effort to archive pages as they are created and archive the pages that they refer to. That way, as the pages that are referenced are changed or taken from the web, a link to the version that was live when the page was written will be preserved.Then the Internet Archive hopes that references to these archived pages will be put in place of a link that would be otherwise be broken, or a companion link to allow people to see what was originally intended by a page's authors.The goal is to fix all broken links on the web . Crawls of supported "No More 404" sites.
– A picture of alleged Navy Yard shooter Aaron Alexis, who was apparently a military contractor, has begun to emerge; now, we're learning about the 12 other people killed in the shooting, which the Washington Post calls "the single worst loss of life in the District" since a 1982 plane crash. The shooting victims were ages 46 to 73, Mayor Vincent Gray says. All were civilians or military contractors, according to the New York Times, and DC police chief Cathy Lanier says at least one was a DC resident. Eight of the victims' names have been released, and the Post has details about their lives: Michael Arnold, 59: He served in the Navy for 29 years and retired as a captain last year. He worked for a government consulting firm and was at the Navy Yard working on a design for amphibious assault ships with a team. He has three sons with his wife of more than 30 years. Arthur Daniels, 51: He was at the Naval Yard for his job installing furniture in federal government buildings. His wife, with whom he has five kids and nine grandkids, calls him "a good father and a hard worker." Sylvia Frasier, 53: Her parents and siblings waited until 10pm last night for news of Frasier, a network-security administrator with the Naval Sea Systems Command. "He killed my sister," sobbed her youngest sister. Kathleen Gaarde, 62: She worked as a financial analyst at the Navy Yard and had just started planning her retirement with her husband of 38 years, with whom she had two children. "Now none of that matters," her husband says. "I already dearly miss her." John Roger Johnson, 73: A neighbor describes him as a civilian who worked for the Navy, and says he was a "smart man" and a "delightful neighbor." Frank Kohler, 50: No comment from his family, but a neighbor describes him as married with two daughters. Vishnu Pandit, 61: No comment from his family, but a neighbor says Pandit and his wife lived in the neighborhood for at least two decades and he was "a very nice man with an Irish setter." Kenneth Bernard Proctor, 46: He had worked for the federal government for 22 years; a civilian utilities foreman at the Navy Yard, he didn't work in the building where he was killed—but he often went there for breakfast. His ex-wife says they still talked every day, and had spoken that morning. They have two teen sons. Eight people were also injured, according to Gray, including three who were shot and five who suffered stress-related injuries; two of the injured were police officers.