Tourists view The Last Column and Slurry Wall in the 9/11 Museum in New York City, April 29, 2018. The first mark was made by Fire Department New York Squad 41, looking to find remains of team members who went missing during recovery, shortly followed by other units. The Last Column, located in the main hall of the museum was returned to its original location as a symbol of loss and remembrance to the First Responders killed during the Sept. 11, 2001 attacks. (U.S. Air Force photo by Staff Sgt. Kristin High)