As the FBI investigates the mass shooting at an Austin bar as a "potential act of terrorism," jitters across the United States are skyrocketing. Three Texas people were killed and 14 wounded Sunday as cops say a gunman opened fire before he was shot dead by police. Shooter Ndiaga Diagne also reportedly had pictures of Iranian leaders in his Texas home. Police shot the gunman dead. Meanwhile, people are taking to social media to express their fears about possible sleeper cells on US soil.