Vice-president Joe Biden said on Saturday the killing of four marines and a sailor in Chattanooga last month was the act of a “perverted jihadist”, a statement that appeared at odds with official comments from investigators.

“These perverse ideologues, warped theocrats, they may be able to inspire a single lone wolf to commit a savage act, but they can never, never threaten who we are,” Biden said. “When this perverted jihadist struck, everyone responded.”

Biden made his comments during a memorial service in Chattanooga. The five servicemen were shot dead by 24-year-old Mohammad Youssuf Abdulazeez, who was himself shot dead by police.

Investigators have said they have not been able to determine a motive behind the attack. The FBI has said it has not been able to determine whether Abdulazeez was “radicalised” before the 16 July attack and has been treating him as a homegrown violent extremist.

Speaking before Biden on Saturday, defense secretary Ash Carter said officials may never know “what combination of disturbed mind, violent extremism and hateful ideology” was behind the shooting.



In the wake of the attack, Carter has called for a review of domestic security procedures for military installations.



On Saturday, he said: “The few who threaten or incite harm to Americans – violent extremists or terrorists, wherever they are – will surely, very surely, no matter how long it takes, come to feel the long arm and the hard fist of justice.”

Abdulazeez opened fire on a military recruiting centre before driving his rented Mustang about seven miles across town to a reserve centre, where he crashed through the gates and killed the servicemen.

Friends and neighbors recalled Abdulazeez as a happy, polite young man. But a picture has also emerged showing a darker side, with Abdulazeez’s family saying he struggled with depression, abused drugs, could not keep a job and was considering bankruptcy.

Abdulazeez spent several months with an uncle in Jordan last year as part of an agreement to get him away from drugs, alcohol and a group of friends his parents considered a bad influence, a person close to the family has said. That person spoke on the condition of anonymity to avoid business repercussions.

Those killed in the attack were navy Petty Officer 2nd Class Randall Smith and four marines: Staff Sergeant David Wyatt, Sergeant Carson Holmquist, Gunnery Sergeant Thomas Sullivan and Lance Corporal Squire “Skip” Wells. Just moments before his death, Wells texted his girlfriend in Savannah the words “ACTIVE SHOOTER”.

Also attending Saturday’s memorial were US senator Bob Corker, Tennessee governor Bill Haslam and Chattanooga mayor Andy Berke.

Biden, whose son Beau died of brain cancer in May, said he could relate to the grief of the victims’ families.

“I didn’t have the privilege of knowing any one of them personally,” the vice-president said. “But oh, I knew them. Confident, determined, trustworthy, compassionate and always, always loyal.

“I knew them. They were my son. And so many other sons I know.”

Beau Biden was a major in a national guard unit that deployed to Iraq in 2008.

The vice-president drew applause for concluding his remarks with a defiant message for anyone who would target the US.

“We have a message for those perverted cowards around the world,” he said. “America never yields, never bends, never cowers, never stands down – [but] endures, responds, and always overcomes. For we are Americans, and never, never underestimate us.

“It’s always been a bad, bad bet to do that.”