WASHINGTON (AP) — Federal investigators were digging Wednesday into the background of a Georgia man who officials say fatally stabbed a Pentagon police officer at a transit station outside the building before being shot and killed himself.

The Pentagon Force Protection Agency identified the slain officer as George Gonzalez, a New York native and Army veteran who served in Iraq and joined the police force three years ago. He died after being attacked Tuesday morning on a bus platform outside the Pentagon.

The burst of violence temporarily placed the U.S. military headquarters on lockdown and jangled the nerves of a region already primed to be on high alert for violence and potential intruders outside federal government buildings.

The FBI was leading the investigation into the violence and the suspect, identified by multiple law enforcement officials as Austin William Lanz, 27, of Georgia. The authorities were examining Lanz’s background, including his criminal history, jail records, financial information and any online accounts as they tried to identify a potential motive for the attack, a law enforcement official said

Gonzalez was ambushed by Lanz, who ran at him and stabbed him in the neck, according to two law enforcement officials who could not discuss the investigation publicly and spoke to The Associated Press on condition of anonymity. Responding officers then shot and killed Lanz.

Lanz had enlisted in the U.S. Marine Corps in October 2012 but was “administratively separated” less than a month later and never earned the title Marine, the Corps said in a statement.

He was arrested in April in Cobb County, Georgia, on criminal trespassing and burglary charges, according to online court records. The same day, a separate criminal case was filed against Lanz with six additional charges, including two counts of aggravated battery on police, a count of making a terrorist threat and a charge for rioting in a penal institution, the records show.

A judge reduced his bond in May to $30,000 and released him, imposing some conditions, including that he not ingest illegal drugs and that he undergo a mental health evaluation. The charges against him were still listed as pending. A spokesman for the Cobb County Sheriff’s Office confirmed that Lanz had been previously held at the agency’s detention center but referred all other questions to the FBI’s field office in Washington.

An attorney who represented Lanz in the Georgia cases didn’t immediately respond to a phone message and email seeking comment, and messages left with family members at Lanz’s home in the Atlanta suburb of Acworth, Georgia, were not immediately returned.

At a Pentagon news conference Tuesday, the PFPA chief, Woodrow Kusse declined to provide even basic information about how the violence had unfolded. He would only say that an officer had been attacked and that “gunfire was exchanged.”

Kusse and other officials declined to rule out terrorism or provide any other potential motive, saying they didn't want to “compromise the ongoing investigation.” But Kusse said "we are not actively looking for another suspect at this time.”

The FBI confirmed only that it was investigating and there was “no ongoing threat to the public” but declined to offer details or a possible motive.

Defense Secretary Lloyd Austin expressed his condolences and said flags at the Pentagon will be flown at half-staff.

“This fallen officer died in the line of duty, helping protect the tens of thousands of people who work in — and who visit — the Pentagon on a daily basis,” Austin said in a statement. “This tragic death today is a stark reminder of the dangers they face and the sacrifices they make. We are forever grateful for that service and the courage with which it is rendered.”

The attack occurred on a Metro bus platform that is part of the Pentagon Transit Center, a hub for subway and bus lines. The station is steps from the Pentagon building, which is in Arlington County, Virginia, just across the Potomac River from Washington. The facility was on lockdown for more than an hour.

An Associated Press reporter near the building heard multiple gunshots, then a pause, then at least one additional shot. Another AP journalist heard police yelling “shooter.”

Austin and Gen. Mark Milley, chairman of the Joint Chiefs of Staff, were at the White House meeting with President Joe Biden at the time of the violence. Pentagon spokesman John Kirby said Austin returned to the building and went to the Pentagon police operations center to speak to the officers there.

In 2010, two officers with the Pentagon Force Protection Agency were wounded when a gunman approached them at a security screening area. The officers, who survived, returned fire, fatally wounding the gunman, identified as John Patrick Bedell.

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Associated Press writers Colleen Long in Washington and Lolita C. Baldor, Matthew Barakat and Sagar Meghani in Arlington, Virginia, contributed to this report.