CHATTANOOGA, Tennessee (AP) -- 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.
Beyond that, little is known about Muhammad Youssef Abdulazeez or what motivated his rampage. Federal authorities were looking into the possibility it was an act of terror, but say there's 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.
Even the exact spelling of his 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 the same high school in Chattanooga several years apart. Javid said Abdulazeez was on the high school's wrestling team and was a popular student.
Javid said he occasionally saw Abdulazeez at the Islamic Society of Greater Chattanooga, but the last time was roughly a year ago.
The shootings took place minutes apart, with the gunman stopping his car and spraying dozens of bullets first at a military recruiting center, then driving to a Navy-Marine training center 7 miles (11 kilometers) 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.
"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.
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."
The U.S. National Counterterrorism Center said it has seen nothing so far to connect Abdulazeez to any terror 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.
The names of the dead were not immediately released.
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.
Associated Press writers Eric Tucker, Ted Bridis and Lolita C. Baldor in Washington; Travis Loller and Kristin M. Hall in Nashville, Tennessee; and Rebecca Reynolds Yonker and Claire Galofaro in Louisville, Kentucky, contributed to this report.