As Americans mourn victims of the mass shooting over the weekend, authorities are focusing on what can be done to prevent “homegrown” extremist attacks. Sunday’s shooting at a popular gay nightclub killed 49 people and injured 53 others. It was the worst mass shooting in U.S. history. The Federal Bureau of Investigation confirmed it had investigated the Orlando gunman, Omar Mateen, on suspicion of possible terrorist ties. FBI Director James Comey told a news conference Monday the FBI conducted interviews with Mateen in 2013 and 2014. Investigators also followed him and reviewed details of some of his contacts and communications. But authorities took no action against him because the FBI did not find any evidence of criminal activity. Comey said the FBI is currently reviewing its practices in the case. But at this point, he said he believes the agency acted appropriately. Comey said the Orlando shooter had “strong indications of radicalization” and may have been “inspired by foreign terrorist organizations.”