An image of an ID badge circulating widely online that shows the suspect in the shooting of the National Guard members says he was assigned to the "Kandahar Strike Force" or "03" unit, one of a number of so-called "Zero Units" that worked closely with U.S. and other foreign forces during the war in Afghanistan. A former senior Afghan military source confirmed to CBS News that the ID badge is authentic.

A U.S. official briefed on the shooting investigation and a former senior Afghan National Defense and Security Forces member told CBS News that the suspect, Rahmanullah Lakanwal, had been part of a "Zero Unit," an Afghan intelligence unit and paramilitary force that worked with the CIA. The units were exclusively composed of Afghan nationals and operated under the umbrella of the National Directorate of Security, or NDS, the intelligence agency established with CIA backing for Afghanistan's previous, U.S.-backed government. They were considered by the U.S. and its international partners to be among the most trusted domestic forces in Afghanistan.

Those units are often labeled "death squads" by human rights groups. The units were known in Afghanistan for their secrecy and alleged brutality, and members were implicated in numerous extrajudicial killings of civilians, particularly during night raids.

The U.S. official briefed on the investigation confirmed the suspect had been disturbed by the casualties in this unit and, more recently, deeply troubled by the killing of his close friend overseas.

The image of the ID badge also carries the words "Firebase Gecko," which was the name of a base used by the CIA and special forces in Kandahar, in southern Afghanistan, inside what was previously the compound of the Taliban's founding leader, Mullah Mohammad Omar.

CIA Director John Ratcliffe said Thursday the suspect had previously worked "with the U.S. Government, including CIA, as a member of a partner force in Kandahar."

Lt. Gen. Sami Sadat, a former commanding general of the Afghan National Special Operations Corps, told CBS News that Lakanwal worked for the "03" unit for eight years. A former senior Afghan general under the U.S.-backed government told CBS News on Thursday that "03 unit, also known as The Kandahar Strike Force (KSF), was under special forces directorate of NDS. They were the most active and professional forces, trained and equipped by the CIA. All their operations were conducted under the CIA command." Lakanwal was part of the unit's operations team, Sadat said.

"He was known for being responsible and professional within his team and had strong anti-Taliban views," Sadat said.

"While we could not establish any connection between him and any terrorist organization, we also cannot completely rule it out," Sadat said. "However, we can confirm that his background does not show any links to terrorists."

Lakanwal's family faced serious threats from the Taliban, which led him to relocate them from their native Khost province to Kabul, Sadat said. In the U.S., Sadat said Lakanwal was "generally calm and maintained a clean record, though he suffered from PTSD."

As a member of a Zero Unit, the suspect would have been virtually guaranteed a route to asylum in the U.S. because members of these elite units were high on the list for Taliban retaliation after the group retook control of the country. Many members of these units played key roles in the August 2021 evacuation from Kabul, in return for a guarantee of space on a flight for themselves and their families out of Afghanistan.

Samantha Vinograd, a CBS News contributor and former Department of Homeland Security counterterrorism official who worked under the Obama administration, said on "Face the Nation with Margaret Brennan" that Afghan evacuees were thoroughly vetted prior to arriving in the U.S. after its withdrawal. 

In Lakanwal's case, the suspect would have been vetted by the CIA prior to joining the Zero Unit, Vinograd said, before referencing comments from national security leaders that suggested he became radicalized after coming to the U.S.

"This horrific tragedy could be the result of an individual that quickly mobilized to violence without any ties to foreign terrorism," said Vinograd. "And, as we have discussed in other cases, trying to find lone actors before they initiate an attack is harder than trying to find a needle in a haystack."

There was no immediate reaction from Afghanistan's current Taliban government, and officials in Kabul did not respond to CBS News' requests for comment on the arrest in Washington.