(AP) - Counterterrorism investigators are trying to figure out why a 24-year-old Kuwait-born man who seemingly had a typical suburban American upbringing attacked two U.S. military sites in a shooting rampage that left four Marines dead.

Muhammad Youssef Abdulazeez of Hixson, Tennessee, did not appear to have been on the radar of federal authorities before the bloodshed Thursday, officials said, and they were still searching for a motive. Abdulazeez was killed by police.

Federal authorities were looking into the possibility it was an act of terrorism but said there was no evidence yet that anyone else was involved.

For months, U.S. counterterrorism authorities have been warning of the danger of attacks by individuals inspired but not necessarily directed by the Islamic State group. Officials have said they have disrupted several such lone-wolf plots.

A federal law enforcement official said authorities were continuing a search of his computer but had not found an extensive online presence and had not uncovered any evidence he was directly influenced by the Islamic State. The official was not authorized to discuss the case publicly and spoke on condition of anonymity.

Residents in the quiet neighborhood where Abdulazeez was believed to have lived in a two-story home said they would see him walking along the wide streets or doing yard work. One neighbor recalled Abdulazeez giving him a ride home when he became stranded in a snowstorm.

"It's kind of a general consensus from people that interacted with him that he was just your average citizen there in the neighborhood. There was no reason to suspect anything otherwise," said Ken Smith, a city councilman who met with neighbors Thursday night.

Abdulazeez got an engineering degree from the University of Tennessee at Chattanooga in 2012 and worked as an intern a few years ago at the Tennessee Valley Authority, the federally owned utility that operates power plants and dams across the South. For the last three months, he had been working at Superior Essex Inc., which designs and makes wire and cable products.

In April, he was arrested on a drunken driving charge, and a mugshot showed him with a bushy beard. In earlier photos, he was clean-shaven.

Hussnain Javid said they graduated a few years apart from Red Bank High School in Chattanooga, where Abdulazeez was on the wrestling team and a popular student.

"He was very outgoing," said Javid, a 21-year-old senior at the University of Tennessee at Chattanooga. "Everyone knew of him."

Javid said he occasionally saw Abdulazeez at the Islamic Society of Greater Chattanooga, but the last time was roughly a year ago.

The gunman on Thursday sprayed dozens of bullets at a military recruiting center at a strip mall in Chattanooga, then drove to a Navy-Marine training center a few miles away and shot up the installation. The bullets smashed through windows and sent service members scrambling for cover.

In addition to the Marines killed, three people were wounded, including a sailor who was seriously hurt. Two of the dead was identified as Sgt. Thomas Sullivan, 40, and Skip Wells, who was in his early 20s. The other victims' names were not immediately released.

"Lives have been lost from some faithful people who have been serving our country, and I think I join all Tennesseans in being both sickened and saddened by this," Tennessee Gov. Bill Haslam said.

FBI agent Ed Reinhold said Abdulazeez had "numerous weapons" but would not give details. He said investigators have "no idea" what motivated the shooter, but "we are looking at every possible avenue, whether it was terrorism, whether it's domestic, international, or whether it was a simple criminal act."

Gen. Ray Odierno, the Army's top officer, said that security at military recruiting and reserve centers will be reviewed, but that it's too early to say whether they should have security guards or other increased protection.

Odierno said there are legal issues involved in allowing recruiters to carry guns. And he said the centers need to be open and accessible to the public.

Brandon Elder, who works at a staffing company in the strip mall where the recruiting office is situated, said he heard what he thought was a jackhammer, and then someone shouted, "He's shooting!"

Elder said he looked out his window onto the parking lot and saw a man in a silver convertible Mustang, a gun propped out the window, spraying bullets into the storefronts.

"He was in front of the recruiting office, just riding up, reversing and driving back," he said. The barrage lasted maybe three or four minutes, and then the driver took off, he said: "It was crazy, surreal, like a movie. Is this really happening?"

On Friday, Gwen Gott added purple ribbons and a flag to a makeshift memorial taking shape outside the strip mall. It included balloons, piles of flowers and a sign staked into the ground: "You were the son of satan. Now you will answer to the son of God."

"I love the service. Without them, where would we be as a country?" Gott said.