US authorities are investigating travel to the Middle East by the suspect in the fatal shootings of four Marines in Tennessee, including at least one trip to Jordan and possibly one to Yemen, a source close to the probe said yesterday.

Mohammod Youssuf Abdulazeez, 24, who the FBI identified as the shooter, was shot to death in a rampage on Thursday at two military facilities in Chattanooga.

The suspect, seen driving an open-top Ford Mustang, sprayed gunfire at a joint military recruiting center in a strip mall, riddling the glass facade with bullet holes, then drove to a Naval Reserve Center about 10 kilometres away, where he killed the four Marines before he died in a firefight with police.

The shooting also injured three people, including a sailor who was critically wounded.

US law enforcement officials said they were investigating whether the suspect was inspired by Islamic State or similar extremists. Islamic State had threatened to step up violence in the holy fasting month of Ramadan, which ended yesterday in the evening.

Suspect graduated in 2012 with an engineering degree

The SITE Intelligence Group, which tracks extremist groups, said Abdulazeez blogged on Monday “life is short and bitter” and that Muslims should not miss an opportunity to “submit to Allah.” While investigators still have no specific evidence of what might have prompted the suspect to carry out the shooting, they believe family or psychological issues may have contributed, according to the source.

His father, Youssuf Abdulazeez, who attended Texas A&M University, according to his Facebook page, appears to be a high achiever. Local media reports citing city records said he is a soil engineering specialist.

The suspect appears to have followed in his father’s footsteps. According to a resume believed to have been posted online by Abdulazeez, he attended high school in a Chattanooga suburb and graduated from the University of Tennessee in 2012 with an engineering degree.