Fire investigators said Tuesday they have still not determined what caused an explosion at a historic Texas hotel that plunged two stories of debris into the basement, blew out windows and doors onto the streets of downtown Fort Worth and left more than 20 people injured, including one person who remained in critical condition. Officials have said that a gas leak was likely involved in Monday's blast, which blew doors and sections of wall into the road in front of the 20-story downtown Sandman Signature Hotel, where authorities said rescuers found several people trapped in the basement. “Obviously there was gas — natural gas — involved," Fort Worth Fire Chief Jim Davis said Tuesday at a news conference.