Three days since the shooting at the El Paso VA clinic, authorities continue their investigation into why an Iraq War veteran and VA employee shot and killed a doctor at the facility before turning the gun on himself.

The veteran has been identified as 48-year-old Jerry Serrato, who killed Dr. Timothy Fjordbak, an El Paso VA psychologist, according to CBS News. Serrato used a .380-caliber handgun in the shooting, according to the FBI, reports NBCDFW.

Fjordbak helped soldiers who returned from combat following the 9/11 terror attacks. The FBI does not have a motive for Serrato's actions but explained that in October 2013 he confronted and threatened Fjordbak.

Douglas Lindquist, head of the FBI's El Paso office, said the 2013 altercation happened at an El Paso supermarket. Serrato allegedly said, "I know what you did, and I will take care of it," at the time. Though the two men were co-workers at the VA clinic in 2013, it is believed they did not work together. The FBI said Fjordbak filed a complaint concerning Serrato after the supermarket incident.

"It was something in public at a grocery store where Mr. Serrato approached Dr. Fjordbak, who did not recognize him, and he made a verbal threat, and that was the extent of the report. As far as we can tell, that was the only connection that they had," Lindquist explained.

Serrato, who served in the National Guard in the late 1980s, was deployed to Iraq from March to July of 2007 after joining the active-duty Army in July 2006, according to the Washington Post. He was medically discharged for an "undisclosed physical ailment in February 2009."

A former VA employee, speaking on condition of anonymity, said Serrato was upset because he had been denied a claim of post-traumatic stress.

Following the shooting, the Fort Bliss complex, including the VA clinic and the William Beaumont Army Medical Center, will undergo a review of its security measures, reports the El Paso Times.

"We're reviewing security measures at all Veteran Affairs Department facilities," U.S. Secretary of Veterans Affairs Robert A. McDonald said when visiting the facilities on Thursday. "We do that frequently anyway, but anytime we have this kind of an incident, obviously we do that."

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