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.Six of the victims were transported to Scott & White Hospital with gunshot wounds. “Their conditions range from quite stable to quite critically injured," Glen Couchman, Scott & White's chief medical officer, said. Couchman said the hospital was not currently in need of blood donations from individuals.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. Soldiers and area residents were ordered to shelter in place, as police pursued reports of a possible second shooter. Several schools in the area were locked down as a precaution.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.In 2009, 13 people were killed and more than 30 wounded in a mass shooting at the base carried out by then-Maj. Nidal Hasan, an army psychiatrist. A U.S. Senate report following the incident described it as the worst attack on American soil since the terrorist attacks of Sept. 11, 2001, although the FBI said Hasan had no formal ties to terrorist groups despite having expressed anti-American viewpoints prior to the shooting.Hassan was sentenced to death after admitting during his August 2013 court martial hearing to the mass shooting. He is now on death row."Ft. Hood was once again stricken by tragedy," Gov. Rick Perry said in a statement. "As Texans, our first priority must be caring for the victims and their families. Ft. Hood has proven its resilience before, and will again.""The scenes coming from Ft. Hood today are sadly too familiar and still too fresh in our memories," Texas Sen. John Cornyn said in a statement Wednesday. " No community should have to go through this horrific violence once, let alone twice."