At least 13 people died Monday after at least one shooter opened fire in a building in the Washington Navy Yard. Officials have identified one shooter, who was shot by authorities at the scene and was counted among the dead, as Aaron Alexis, a 34-year-old Navy employee whose work status changed earlier this year. Police were looking to identify one other possible gunman, someone at the scene who was wearing a military-style uniform. The motive was not yet known. At least four people were wounded, but officials said three of them are expected to make a full recovery. Read full story here.

Colorado’s flood evacuees have begun to return home Monday, but many homes and vehicles have been destroyed, and a layer of mud covers the affected areas. Rescuers continue to search for the hundreds or thousands of people missing — estimates vary because of a lack of phone or Internet service to reach people who are presumed to be OK — and they began to drop supplies to people in communities cut off by floodwater.

Engineers on Monday successfully removed the hull of the Costa Concordia shipwreck that crashed off the coast of Italy in January 2012. Officials said getting the liner upright is taking longer than expected but should be completed by Tuesday morning. The shipwreck killed 32 people more than a year ago when the boat slammed into a reef near Giglio Island, and the captain of the ship currently is on trial for manslaughter. Read full story here.

United Nations inspectors determined Monday that the nerve gas sarin was used in the Aug. 21 attack in Syria that United States officials say killed almost 1,500 people. The report did not say who was behind the attack. Also on Monday, President Barack Obama cleared the way to give non-lethal assistance to the Syrian rebels and personal protective equipment to international aid organizations working in Syria.

Information is from the Associated Press.