CHATTANOOGA (Tennessee) • He was an "all-American kid" from an "average" family, shocked friends and acquaintances said of 24-year-old Kuwaiti-born Mohammod Youssuf Abdulazeez, who gunned down four Marines in a rampage in Tennessee.

Investigators are treating Thursday's deadly shooting as an act of "domestic terrorism" in the heart of the Bible Belt. Abdulazeez himself died in a shoot-out with police.

According to the Federal Bureau of Investigation (FBI), he was a Kuwaiti-born Jordanian who became a naturalised US citizen. A local newspaper said he was a graduate of Red Bank High School, whose quotation on his graduation yearbook page was: "My name causes national security alerts. What does yours do?"

His neighbours in Hixson, the suburb of Chattanooga where he grew up, said he seemed to have been an all-American boy, handsome and polite, normally in a T-shirt and jeans.

He was arrested in April for a traffic offence, but was otherwise thought not to have been in trouble with the police.

Hours after his killing spree, the authorities were still piecing together a portrait of the former high school wrestler with an engineering degree to explain why he might have turned into a killer.

A woman who attended high school with Abdulazeez said he was a quiet, well-liked student.

"He was friendly, funny, kind," Ms Kagan Wagner told the Chattanooga Times Free Press. "I never would have thought it would be him," she added.

"I mean, he seemed like the all-American kid," Abdulazeez's mixed martial arts coach Scott Schrader told CNN, adding that he was "never loud, never boisterous, never got out of line".

Mr Dean McDaniel, 59, a neighbour, said he had known Abdulazeez for the past dozen years or so, when the family moved into the neighbourhood.

He said that two of Abdulazeez's sisters used to babysit his children. He remembered the siblings as well behaved and polite, adding you could tell that "they had strict parents".

Abdulazeez's father, who shares his name, works for the city's public works department, where he was appointed as a "special policeman".

A Facebook page which appeared to belong to his mother shows a cheerful photo of Abdulazeez smiling at his graduation as he hugged an elderly woman.

Other Facebook photos show the once clean-cut Abdulazeez had grown a beard recently.

AGENCE FRANCE-PRESSE, NEW YORK TIMES