The Kuwait-born engineer accused by US officials of murdering four marines in Tennessee had previously worked at a nuclear power station in Ohio just two years ago.
Mohammod Youssuf Abdulazeez, 24, a naturalised US citizen, who died after a firefight with police, is suspected of killing Gunnery Sgt Thomas Sullivan, Staff Sgt David Wyatt, Sgt Carson Holmquist and Lance Cpl Squire 'Skip' Wells in two separate incidents.
The attacks, on two military sites in Chattanooga, Tennessee, took place about 30 minutes apart on Thursday with the suspect stopping his silver Mustang convertible and spraying bullets at a naval recruitment centre.
Yesterday Todd Schneider, a spokesman for FirstEnergy Corp (FE.N), said Abdulazeez worked at the Perry Nuclear Power Plant's administrative offices in 2013, reported Reuters.
He confirmed that Abdulazeez was a conditional employee that was dismissed after general training because, "he did not meet the minimum requirements for ongoing employment".
Although Schneider did not say why Abdulazeez was dismissed the New York Times have reported that he had failed a drugs test.
He also added that Abdulazeez was never granted access to the secure area of the plant.
Three people were also injured in the attack, including a US Navy sailor and US officials are investigating as "an act of terrorism" who say that Abdulazeez was shot dead by police in the shoot-out that ensued.
Part of the investigation is focusing on a trip he made to the Middle East last year, including a period spent in Jordan, where he also held citizenship.
And US law enforcement agencies are also investigating possible links to Islamic State (Isis) group after a Twitter account reportedly connected to Isis was believed to have claimed credit for the shooting.
Just this week the engineer had written in a blog that "life is short and bitter" according to Sky News.
The SITE Intelligence Group, which tracks extremist groups, said that Abdulazeez blogged the message earlier this week and added that Muslims should not miss an opportunity to "submit to Allah".