CHATTANOOGA, Tennessee -- Counterterrorism investigators are trying to figure out why a 24-year-old Kuwait-born man, who by accounts lived a typical life in suburban America, attacked two military facilities in a shooting rampage that killed four Marines.
Mohammod Youssuf Abdulazeez had not been on the radar of federal authorities until the bloodshed and authorities said 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 say there is no evidence yet that anyone else was involved - or that the public is in any danger.
Abdulazeez travelled to Kuwait and Jordan recently, CBS News has learned. Officials will need to track down who he visited, stayed with, met with and communicated with while overseas. That will bring in police and intelligence services of Kuwait and Jordan - both are U.S. allies and cooperation is expected.
Investigators have started to remove computers believed used by Abdulazeez, CBS News has learned. So far, there is no immediate link to the Islamic State of Iraq and Syria (ISIS) or other terrorist groups but officials stress this is very early in the investigation. The forensic search of computers, phones and on line activity may take some time.
If investigators find that Abdulazeez was indeed inspired by ISIS, CBS News senior security contributor Michael Morell said it would be "the most significant ISIS-inspired attack" on U.S. soil to date.
Officials have said they do not know why the shooter targeted the facilities and have not said what weapons he used.
CBS Boston says one of the Marines killed was Gunnery Sgt. Thomas Sullivan, 40, a native of Springfield, Massachusetts. The station cites the India Battery 3rd Battalion 12th Marines Facebook page. According to MassLive.com in Springfield, Sullivan served two tours of duty in Iraq, and earned a Purple Heart, CBS Boston adds.
Even the exact spelling of Abdulazeez's first name was not clear: Federal authorities and records gave at least four variations. Residents in the quiet neighborhood where he is believed to have lived said they didn't know him or his family well.
CBS News correspondent Jericka Duncan reports Abdulazeez's high school yearbook shows his senior photo, with the quote, "My name causes national security alerts. What does yours do?"
Officials confirmed to CBS News that his father was under investigation several years ago over possible ties to a foreign terrorist organization. However, he was later taken off a terror watch list after the investigation didn't pan out.
Hussnain Javid, a 21-year-old senior at the University of Tennessee at Chattanooga, said Abdulazeez studied electrical engineering at the same college and they both graduated the same high school several years apart. Javid said Abdulazeez was on the high school's wrestling team and was a popular student.
Kevin Emily, Abdulazeez's high school wrestling coach, thought of himself as a father figure to the teens on his team. He told Duncan he spent much of Thursday fielding phone calls from former students who heard the news.
"I was numb when I heard it because I heard it from one of my wrestler's parents," Emily said. " ... They're just like, 'Coach, can you believe it? Can you believe Muhammad did that?"'
"I don't have any bad words to say about him as an individual that wrestled for me and neither do they," Emily said. "So we're all in shock and we're all hurt."
The Tennessee Valley Authority confirmed Abdulazeez had been an intern at the public utility a few years ago.
"He was very outgoing," Javid said. "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. In April, he was arrested on a first offense drunken driving charge. The status of that case wasn't immediately clear.
The shootings took place minutes apart, with the gunman stopping his car and spraying dozens of bullets first at a recruiting center for all branches of the military, then driving to a Navy-Marine training center 7 miles away, authorities and witnesses said. The attacks were over within a half-hour.
In addition to the Marines killed, three people were reported wounded, including a sailor who was seriously hurt.
A U.S. official said there was no indication Abdulazeez was on the radar of federal law enforcement before the shootings. The official was not authorized to discuss the case and spoke on condition of anonymity.
Authorities would not say publicly how the gunman died, but the U.S. official said investigators believe Chattanooga police fired the shot that killed him. At least one military commander at the scene also fired at the gunman with his personal weapon, but forensic investigators determined that police killed him, the official 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."
Reinhold also told a news conference late Thursday that "there is no indication at this point that anybody else was involved."
Within hours of the bloodshed, law officers with guns drawn swarmed what was believed to be Abdulazeez's house and two females were led away in handcuffs.
The U.S. National Counterterrorism Center said it has seen nothing so far to connect Abdulazeez to any terrorist organization, but intelligence officials are monitoring the investigation closely. The Islamic State group has been encouraging extremists to carry out attacks in the U.S., and several such homegrown acts or plots have unfolded in recent months.
The names of the dead were not immediately released. In addition to the wounded sailor, a Marine was hit in the leg but not seriously hurt, and a police officer was shot in the ankle, authorities said.
In Washington, President Barack Obama pledged a prompt and thorough investigation and said the White House had been in touch with the Pentagon to make sure military installations are being vigilant.
"It is a heartbreaking circumstance for these individuals who served our country with great valor to be killed in this fashion," Obama said.