Defense Secretary Chuck Hagel called the fatal shooting at Fort Hood on Wednesday a “terrible tragedy,” as military leaders and others in the administration sought to find out how, and why, this could have happened again.

Details are still emerging about the shooting, which comes more than four years after Nidal Hasan killed 13 people and injured dozens at the same military post. President Obama, speaking briefly in Chicago, said it has “reopened” the pain of what happened in 2009.

“We’re heartbroken that something like this might have happened again,” Obama said, while noting officials are still gathering the facts, and his national security team is working closely with the Defense Department and FBI.

According to one source, at least four people were killed, including the shooter, and at least 14 people were injured on Wednesday.

Texas lawmakers asked Americans to keep the victims and their families in their prayers.

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“Tonight, Texans’ hearts are once again very heavy,” Sen. John Cornyn, R-Texas, said. “The scenes coming from Ft. Hood today are sadly too familiar and still too fresh in our memories. No community should have to go through this horrific violence once, let alone twice.”

Army Secretary John McHugh, who was at the Capitol for a reception and left for the Pentagon to be briefed on Fort Hood after reports of the shooting emerged, called the incident a “tragedy” and an “emotional moment.”

Obama noted that many of those at Fort Hood have served multiple tours in Iraq and Afghanistan.

“We don’t yet know what happened tonight but obviously that sense of safety has been broken once again. We need to find out exactly what happened,” he said.