Danny Fitzsimons, from Roch- dale, is serving a 20-year sentence in Iraq for murdering Paul McGuigan, 37, and Australian Darren Hoare, 37, within hours of arriving in Baghdad in 2009.
All three were employed by G4S-owned ArmorGroup.
After the inquest, Mr McGuigan’s mother, Corinne Boyd-Russell, 62, from Innerleithen in the Borders, criticised the firm for its failings and said they had yet to apologise to her family.
“I have always said that Danny pulled the trigger but he’s not the only one with my son’s blood on his hands,” she said.
“G4S is the third-largest private-sector employer in the world. It’s time these rich and powerful organisations were properly accountable and that should start with an apology to all of us, to Paul’s family.
“We’ve never had an apology after five and a half years.”
Fitzsimons, a former soldier in the Parachute Regiment, had been dismissed from the army and was on the run for a string of offences when the security firm took him on without vetting him properly.
A steroid user, described as violent and unpredictable, especially when drunk, Fitzsimons held extreme racist views and, according to one doctor’s assessment, only showed any excitement when talking about involvement in football hooliganism and firing guns.
In pages of writings recovered by police from his home he had written: “I have lived a life of violence. Any chance I have to do someone I will take it.”
He was being dealt with by the Probation Service after offences of assaults, robbery and possession of ammunition but there were “significant missed opportunities” to properly assess and supervise him, the inquest heard.
While on bail he got the job with G4S, flew out to Baghdad, was issued with weapons, got drunk and shot dead his two colleagues at a base, less than 12 hours after arriving in the Green Zone of the Iraqi capital.
Fitzsimons, 34, had got into “banter” with Mr McGuigan, a former Royal Marine from Peebles, and Mr Hoare and later claimed he killed the two men in self defence after they attacked him. But no defence injuries were discovered on either man and Fitzsimons was later found guilty of both murders by a court in Iraq.
Each victim was shot three times with a Glock 9mm pistol – Mr McGuigan, a father of two, shot twice in the chest and once at point blank range in the mouth. Fitzsimons also shot and injured an Iraqi security guard.
In a statement G4S said: “The death of Paul McGuigan came as a profound shock to G4S. Paul McGuigan was a son, a partner, a father and a colleague, and G4S extends its sincerest sympathies to his family for the anguish they have suffered as a result of his loss. Industry standards for the recruitment of private security operators in high-threat environments have advanced significantly in the years following this tragic incident.”