Four U.S. Marines were killed on Thursday by a gunman who opened fire at two military offices in Chattanooga, Tennessee, before being fatally shot in an attack officials called a brazen, brutal act of domestic terrorism.
The FBI named the suspect as Mohammod Youssuf Abdulazeez, 24, but said it was too early to speculate on a motive for the rampage, which comes at a time when U.S. military and law enforcement authorities are increasingly concerned about the threat posed by 'lone wolves' to domestic targets.
"We are treating this as an act of domestic terrorism," Bill Killian, the U.S. Attorney for the Eastern District of Tennessee, said earlier, adding that no official determination of the nature of the crime had yet been made and the Federal Bureau of Investigation has not ruled anything out.
"While it would be premature to speculate on the motives of the shooter at this time, we will conduct a thorough investigation of this tragedy and provide updates as they are available," the agency said in a statement.
NBC reported he was a naturalized American born in Kuwait.
U.S. officials said law enforcement authorities are investigating whether he was inspired by Islamic State or a similar militant group.
President Barack Obama offered his condolences to the victims' families and said officials will be prompt and thorough in getting answers on the shootings.
"It is a heartbreaking circumstance for these individuals who have served our country with great valor to be killed in this fashion," he said in a statement from the Oval Office.
The Department of Homeland Security was stepping up security at certain federal facilities and supporting the FBI investigation, DHS Secretary Jeh Johnson said in a statement.
Chattanooga is a city of about 173,000 people along the Tennessee River in the southeast of the state.
The suspect, seen driving an open-top Ford Mustang, is believed to have first gone to a joint military recruiting center in a strip mall and sprayed it with gunfire, riddling the glass facade with bullet holes.
"Everybody was at a standstill and as soon as he pulled away everyone scrambled trying to make sure everyone was OK," said Erica Wright, who works two doors down from the center.
Armed forces recruiting centers are often located in shopping centers and other prominent places.
The gunman then drove off to a Naval Reserve Center about 6 miles (10 kilometers) away, fatally shooting the four Marines before being shot and killed in a firefight with police.
Three others were wounded in the attacks, including a police officer reported in stable condition and a Marine.
The shootings began at about 10:45 A.M. local time and ended about 30 minutes later.
Chattanooga Police Chief Fred Fletcher told a news conference many officers converged to engage "this brazen criminal and one of those officers was injured by gunfire" from the suspect. The suspected shooter is believed to have lived in the area and acted alone, police said.
Police blocked access to the street where the suspected gunman lived in an upscale suburb. Only residents with photo IDs were allowed to pass and all cars coming and going were stopped.
Mary Winter, president of the Colonial Shores Neighborhood Association, said she had known Abdulazeez and his family for more than 10 years and was stunned at the crime.
"We're all shocked and saddened," Winter said. "He never caused any trouble. We can't believe that this happened. We were just planning to have a swim team banquet tonight."
Chattanooga Mayor Andy Berke lashed out at the gunman in an interview with cable news channel CNN.
"This was an individual who was motivated to do significant damage," he said. Local media said memorial services for the victims would be held in various Chattanooga churches tonight.