The man who authorities say killed four Marines in an attack on a military recruiting center and another U.S. military site was a 24-year-old, Kuwait-born engineer who had not been on the radar of federal authorities until the bloodshed.
Beyond that, little is known about Muhammad Youssef Abdulazeez of Hixson, Tennessee, or what motivated his rampage.
Federal authorities were looking into the possibility it was an act of terrorism, but there is no evidence yet that anyone else was involved - or that the public is in any danger.
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
According to MassLive.com in Springfield, Sullivan served two tours of duty in Iraq, and earned a Purple Heart, CBS Boston adds.
People gathered at a local church Thursday night to pray for the shooting victims, reports CBS News correspondent Dean Reynolds.
Even the exact spelling of the gunman's first name was not clear: Federal authorities and records gave at least four variations. Residents in the neighborhood where Abdulazeez is believed to have lived said they didn't know him or his family well.
Hussnain Javid, a 21-year-old senior at the University of Tennessee at Chattanooga, said Abdulazeez studied electrical engineering at the same college. They both graduated from Red Bank High School in Chattanooga several years apart. Javid said Abdulazeez was on the high school's wrestling team and was a popular student.
Abdulazeez was not on any U.S. terror list and the FBI said no connections have been found to the Islamic State of Iraq and Syria (ISID) or Muslim extremists.
A U.S. official told The Associated Press 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.
CBS News correspondent Jericka Duncan reports Absulazeez'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.
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."
"Obviously, we're still at the beginning of this investigation," he said. "We will explore any possibility and that includes whether or not anyone else was involved."
U.S. Attorney Bill Killian told the news conference that "as far as we know at this juncture, there are no safety concerns for the general public."
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.
Authorities would not say publicly how the gunman died, but a 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. An autopsy will determine whose shot ended his life, authorities added.
The Associated Press contributed to this report.