The Chattanooga, Tennessee shooter likely purchased his firearms to carry out the fatal attack at two US military facilities legally, among them two riffles and a handgun," the Federal Bureau of Investigation (FBI) agent leading the investigation into the attacks, Ed Reinhold, said during a press conference on Friday.
"He [the shooter] did have at least two long guns, which would be considered rifles or shotguns, and he did have one hand gun that we're aware of," Reinhold said. "Again we are continuing to explore those possibilities, some of the weapons were purchased legally and some of them may not have been, we will examine that."
He added that FBI would look into possibility of the shooter Muhammad Youssef Abdulazeez being inspired by ISIL.
"That [ISIL links] is a possibility that we will explore," Reinhold said. "At this time we have no indication that he was inspired by or directed by anyone other than himself."
On Thursday, Abdulazeez, 24, attacked two Naval Reserve facilities in Chattanooga, killing four marines and wounding three more people. He died in the assault.
The FBI is working to reconstruct the circumstances of the tragedy, and is investigating the incident as domestic terrorism.
Earlier on Friday, media reported US authorities have been investigating Abdulazeez's trip to the Middle East in 2014 for possible connections to the IS.
"We are exploring all possibilities to include any contacts overseas," Reinhold said.
US authorities said Abdulazeez has not been listed in the US terrorism database, according to media reports. However, several years ago his father had been probed for possible links to a terrorist organization.