Last Updated Jul 18, 2015 7:18 PM EDT
The gunman in Thursday's deadly rampage in Chattanooga, Tennessee, told his co-workers that he had been at a gun range as recently as last month, law enforcement sources told CBS News.
Co-workers of Mohammod Youssuf Abdulazeez told investigators that he said he frequented a local gun range with several friends, CBS News homeland security correspondent Jeff Pegues reports.
Abdulazeez's co-workers told investigators that he said the group shot rifles, BB guns and pistols as recently as June, Pegues reports.
Abdulazeez slaughtered four Marines and wounded three others in the attacks, including a sailor who died Saturday in a hospital. Authorities said he wore a vest with extra ammunition, wielding at least two long guns - either rifles or shotguns - and a handgun.
Investigators believe Abdulazeez became a U.S. citizen in 2003, Pegues reports.
They also believe that he traveled on at least four separate occasions to Jordan with the last recorded date of travel between April 2014 and November, Pegues reports. Investigators at this time do not have any information to suggest that the trips were connected to any violent extremist activities.
On Friday night, the FBI and U.S. Department of Homeland Security issued an intelligence bulletin warning of the potential for lone wolf style attacks, Pegues reports. The bulletin says, "The FBI and DHS are not aware of any further credible threats against the U.S. military or the homeland related to this attack."
The bulletin goes on to say that "it is difficult to assess triggers that will contribute to U.S.-based violent extremists attempting acts of violence" and that "lone offenders present law enforcement with limited opportunities to detect and disrupt plots, which frequently involve widely available small arms against perceived targets of opportunity."
The image of Abdulazeez described by investigators doesn't square with the seemingly pedestrian suburban man that neighbors and classmates knew: A clean-cut wrestler, the brother of a tennis player, the son of parents who drove no-frills cars. He was a man who played with the neighborhood kids growing up, and gave a lift to a neighbor who became stranded in a snowstorm.
Just days before the shootings, Abdulazeez was seen dribbling a soccer ball in his yard, and he told two longtime friends he was excited and upbeat about his new job at a company that designs and makes wire and cable products.
"Everything seemed fine. He was normal. He was telling me work was going great," said Ahmed Saleen Islam, 26, who knew Abdulazeez through the Islamic Society of Greater Chattanooga and saw him at the mosque two or three nights before the attacks.
"We are so shocked and angry," Islam told The Associated Press. "We wish he would have come to us."
Hailey Bureau, 25, recalled sitting next to Abdulazeez in high school because their last names were close alphabetically. She said she broke down Thursday when she learned he was the gunman, saying, "It's so shocking. I imagine him the way I knew him then, laughing and smiling."
Bureau recalled Abdulazeez's sense of humor, evident in a wry quote next to his yearbook photo, one that has since taken on bitter irony: "My name causes national security alerts. What does yours do?"
The 24-year-old Kuwait-born man opened fire on two U.S. military sites in Chattanooga on Thursday. It's not clear what set him on the path to violence that ended with him being gunned down by police.
On Saturday, Navy Petty Officer 2nd Class Randall Smith, a reservist serving on active duty at the Chattanooga center, died, bringing the death toll to five.
Smith grew up in the northwest Ohio city of Paulding and joined the military after attending college in Ohio, his grandmother Linda Wallace said before his death. He was married and had three young daughters.
Abdulazeez did not appear to have been on federal authorities' radar before the bloodshed Thursday, officials said. But now counterterrorism investigators are taking a deep look at his online activities and foreign travel, searching for clues to his political contacts or influences.
"It would be premature to speculate on exactly why the shooter did what he did," FBI agent Ed Reinhold said. "However, we are conducting a thorough investigation to determine whether this person acted alone or was inspired or directed."
In the quiet neighborhood in Hixson, Tennessee, where Abdulazeez lived with his parents in a two-story home, residents and former classmates described an ordinary suburban life.
"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.
However, court documents allege it was an abusive and turbulent household.
Abdulazeez's mother, Rasmia Ibrahim Abdulazeez, filed a divorce complaint in 2009 accusing her husband, Youssuf Saed Abdulazeez, of beating her repeatedly in front of their children and sexually assaulting her. She also accused him of "striking and berating" the children without provocation.
Weeks later, the couple agreed to reconcile, with the father consenting to go to counseling.
Abdulazeez graduated from Red Bank High School in Chattanooga, where he was on the wrestling team.
Bilal Sheikh, 25, said he had known Abdulazeez since they were teenagers, and they often played basketball together. He saw his friend at the mosque last weekend, as they came to pray and as part of the services to celebrate Ramadan.
"I'm in total shock, like everyone else," Sheikh said, later adding, "He was always the most cheerful guy. If you were having a bad day, he would brighten your day."
Islam and Sheikh both said that in the years they had known Abdulazeez, he never expressed any negative feelings about the United States or members of the military.
"He never said anything that would have been a red flag," Sheikh said. "I have so many questions in my head. I want to know why? What made him crack all of a sudden? It's mindboggling."