Muhammad Youssef Abdulazeez, the gunman who killed five Marines at two military facilities in Chattanooga, Tenn., was briefly employed at a nuclear power plant in Northeast Ohio in 2013.

Abdulazeez, an electrical engineer who graduated from the University of Tennessee in Chattanooga in 2012, was a conditional employee of the Perry Nuclear Power Plant near Cleveland, Ohio, between May 20 and May 30, 2013, but he was let go after failing FirstEnergy's background check, according to The Plain Dealer.

"He failed to meet our minimum requirements for employment," spokeswoman Jennifer Young said. "In the 10 days during the screening process, he was classified as a conditional employee."

While background checks were being conducted, Abdulazeez and other applicants participated in general training classes at the plant's administration building, and he was not allowed into the plant's security areas, according to Young.

"He was never inside the plant. He did not have any company documents. He was received like any member of the public," she said.

The 24-year-old Kuwait-born shooter was recognized by former plant coworkers who immediately informed managers. The company then informed the Nuclear Regulatory Commission on Friday, according to The Plain Dealer

Some, like former CIA officer Josh Katza, insist Abdulazeez "is going to be shown to have links to ISIS," but the FBI says there is no evidence of a connection to terror groups, CNN reported.

Abdulazeez's father had been under investigation several years ago for donating money to an organization with a possible connection to a foreign terrorist organization, but was later cleared and removed from the terror watchlist, according to The New York Times.

Abdulazeez traveled to Jordan and possibly other Middle Eastern countries for seven months last year, and upon return, a friend noted that he had become a "different type of person."

The night before the attack, Abdulazeez sent a religious text message referencing an Islamic verse, Hadith 38, which says, "Whosoever shows enmity to a friend of Mine, I will indeed declare war against him," BBC News reported. He had also spoken out against conflicts in the Middle East, including Israeli bombing campaigns in Gaza and the Syrian civil war.

The FBI said it continues to investigate the attacks as an act of terrorism and added that it is "premature" to speculate on his motive, Reuters reported.