A shooting at Fort Hood on Wednesday left four people dead, including the gunman, and others critically injured, officials said. The shooter, identified as 34-year-old soldier Ivan Lopez, died of a self-inflicted gunshot wound, the Justice Department said. Emergency crews, FBI and SWAT teams were called in to the base following the shooting, which occurred at approximately 4:30 p.m. at a medical support building on the sprawling base. President Barack Obama said the White House was monitoring reports of the shooting. "We're following it closely. The situation is fluid right now," Obama told reporters in Chicago, adding that investigators would "get to the bottom of exactly what happened." "We're heartbroken something like this might have happened again," the president said.