Mohammod Youssuf Abdulazeez, who is suspected of killing five Marines in Tennessee last week, was in Qatar at least once during a 2014 trip to the Middle East, according to two U.S. government sources who spoke to Reuters on Monday.
The sources said reasons for the stopover were still unknown.
On a seven-month trip to visit family in Jordan, it is uncertain how long he may have spent in the Qatari capital which is home to jihadist supporters as well as a U.S. air base.
Abdulazeez, a Kuwaiti-born naturalized U.S. citizen, was killed in a gunfight with police on Thursday after he sprayed gunfire at a military recruiting center in Chattanooga, then drove to a nearby Naval Reserve Center where he shot and killed four Marines. Three people were wounded, including a sailor who died on Saturday.
The FBI said on Friday it would investigate Abdulazeez’s visit to Jordan and whether he left Jordan to visit other countries before coming home, though investigators had earlier indicated they don't have "anything that directly ties" Abdulazeez to any foreign terrorist organizations.
Experts have said his behavior fits the mold of attacks Islamic State (ISIS) has called for.
The shooting in Tennessee followed a series of attacks, or thwarted attacks, in the United States and other countries by Muslims claiming to be inspired by Islamic State or other jihadist groups.
Abdulazeez apparently did not use a laptop but could have read jihadist propaganda on his smart phone, the sources close to the investigation and a second source told Reuters.
More details emerged on Monday about Abdulazeez's possible frame of mind leading up to the attacks. He had drug abuse problems and was worried about debt, according to his family and a diary he left behind, ABC News reported, citing a family representative.
A close friend of Abdulazeez said on the weekend that Abdulazeez texted him a link to an Islamic verse hours before the attack, including the line: "Whosoever shows enmity to a friend of Mine, then I have declared war against him."
The shooter was also allegedly upset about the 2014 war between Israel and Hamas in Gaza and the civil war in Syria.