Firefighters are scouring the wreckage of a historic Fort Worth hotel as they investigate the cause of a massive explosion that shattered windows, littered the streets with debris and injured 21 people, including one critically. The Monday blast blew doors and sections of wall into the road in front of the 20-story downtown Sandman Signature Hotel, where authorities say rescuers found several people trapped in the basement. By evening, officials said everyone seemed to have been accounted for, though the search continued overnight. The fire department is working with state inspectors and utility workers to determine the exact cause of the explosion, though authorities believe a gas leak was to blame.