Abdulazeez had a handgun and two long guns in his possession when police in the Tennessee city killed him Thursday, and another rifle was seized when police searched his home, the official said.
The 24-year-old engineering graduate wore a "load-bearing vest" that allowed him to carry extra ammunition, said Ed Reinhold, special agent in charge of the regional FBI office.
It does not appear that the weapons were purchased recently, the law enforcement official said. Reinhold said earlier Friday that "some of the weapons were purchased legally and some of them may not have been."
Abdulazeez attacked a military recruiting station in a shopping plaza and a Naval reserve office seven miles away, killing four Marines and wounding a Chattanooga police officer, a Marine recruiter and a Navy sailor.
Authorities are working to figure out why Abdulazeez -- an accomplished student, well-liked peer, mixed martial arts fighter and devout Muslim -- went on the killing spree.
U.S. Attorney Bill Killian said the shootings are being investigated as an "act of domestic terrorism," but he noted the incident has not yet been classified as terrorism.
Reinhold said there is nothing to connect the attacker to ISIS or other international terror groups. Abdulazeez was not on any U.S. databases of suspected terrorists.
He was not known to have trouble with the law except for a DUI arrest in April. He apparently was not active on social media -- one of the common ways police investigate terrorism.
The father of Abdulazeez was investigated -- and cleared, twice -- as part of an FBI investigation into terrorism financing, law enforcement officials said.
Officials stressed that Abdulazeez
' father was one of many people investigated for their funding of overseas charities, especially after the September 11, 2001, terrorist attacks. Most of them were never charged with a crime.
The president of the Islamic Society of Greater Chattanooga told CNN affiliate WDEF that Abdulazeez' father called him after the shooting.
"He was in the dark on what his son has done, he's very devastated," Bassam Issa said. The father "actually apologized for what his son did to the community at large and to the Muslim community and I told him we all feel distraught, we all feel shocked."
'Something happened over there'
Abdulazeez was a devout Muslim but didn't appear to be radical, according to some who knew him. He was born in Kuwait but became a naturalized American citizen.
Jordanian sources said Abdulazeez had been in Jordan as recently as 2014 visiting an uncle. He had also visited Kuwait and Jordan in 2010, Kuwait's Interior Ministry said.
A longtime friend said Abdulazeez changed after spending time in the Middle East and "distanced himself" for the first few months after returning to Tennessee.
"Something happened over there," Abdulrazzak Brizada told CNN, saying, "he never became close to me like he was before he went overseas... I'm sure he had something that happened to him overseas."
Witness: 'It was insane'
Gina Mule witnessed one of the shootings as she opened up her restaurant in a small plaza along Chattanooga's Lee Highway. She said she heard a "pow, pow, pow!"
"He never got out of the car. He had a big, huge, high-powered rifle, and he was unloading shots right into the recruiters," she said, referring to the offices of an armed forces recruiting center. "There had to be 20 to 30 shots."
Watching from a nearby hair salon, April Grimmett saw a man ducking between cars.
"Shortly after that, we heard the (shots). It was very loud and very fast," she said. "It was insane."
Over the next half-hour, Abdulazeez, a graduate of the University of Tennessee at Chattanooga, drove his rental car to a Navy operational support center 7 miles away, a law enforcement official said.
Chattanooga police Chief Fred Fletcher told CNN that police followed and engaged Abdulazeez somewhere on the road after that, then again at the second site. He said authorities are still trying to determine whether police saw him ram the gates of the center, get into the facility and shoot and kill the four Marines.
He kept police at bay for some time before being killed.
A senior Defense official told CNN several of the Marines in the recruiting center were combat veterans.
When the shooting broke out, they went into combat mode, had everybody drop to the floor, and then "cleared the room" by having everyone go out the back, the official said. All seven people in the center survived, and reports indicate those Marines helped save lives.
"All indications are he was killed by fire from the Chattanooga police officers," Reinhold told reporters Friday. "We have no evidence he was killed by self-inflicted wounds."
The military released the names of the four slain Marines: Thomas Sullivan, a native of Hampden, Massachusetts; Squire "Skip" Wells, a native of Marietta, Georgia; David Wyatt, a native of Burke, North Carolina; and Carson Holmquist of Grantsburg, Wisconsin.
What was the security situation?
While no one saw this carnage coming, authorities are painfully aware that such threats do exist. Terrorists around the world have unleashed venom, and sometimes attacks, on U.S. troops, citizens and the government. The United States has responded with force, going after groups such as ISIS
and al Qaeda.
Much of that back-and-forth has happened overseas, including attacks on Iraq
and Afghanistan. But the home front hasn't been completely safe, in particular military installations.
The bloodiest cases were the September 11, 2001, terrorist attacks
and then-Army psychiatrist Maj. Nidal Malik Hasan's 2009 massacre at the Fort Hood, Texas
, base that left 13 dead and 32 injured.
Chattanooga's Muslim community has been deeply shaken, given that Abdulazeez regularly attended mosques there. Bassam Issa, the local Islamic Society's president, urged Muslims to attend an interfaith gathering Friday night to show solidarity after what he called an act "of cowardice and hate."
"We don't see our community center as a 'Muslim' community," Issa said, noting that his group's leaders are working with law enforcement and local leaders. "We are Chattanoogans first, and we see ourselves as part of the larger community of Tennesseans grieving (this) act."