Paul McGuigan and Darren Hoare were murdered by Danny Fitzsimons in 2009.
The former paratrooper from Rochdale is serving a 20-year sentence in Baghdad.
G4S international recruitment manager Rebecca Walker told Mr McGuigan's inquest she allowed Fitzsimons to be deployed without several checks.
During his trial in 2011, Fitzsimons told the Iraqi court he had been suffering from post-traumatic stress disorder and claimed he acted in self-defence after a fight broke out.
He admitted killing Mr McGuigan, a former Royal Marine from Peebles in the Scottish Borders who had been living in Tameside, Greater Manchester and Australian Mr Hoare.
Ms Walker told the inquest in Stockport she had interviewed Fitzsimons for his job in July 2009.
She said normal procedure would have seen a successful candidate vetted before being deployed.
She was then shown an email dated on the day of his interview, which showed a deployment date of early August.
She accepted that Fitzsimons, who she said had come across as engaging, smart and professional in his interview, was deployed to Iraq without up-to-date references, with no Criminal Records Bureau check and with a forged medical certificate.
She admitted that with hindsight, she had been "naive" not to have checked the medical certificate with the doctor who was supposed to have signed it.
The inquest continues.
The woman responsible for hiring a security guard who shot two colleagues dead in Iraq was "naive" not to check what turned out to be a forged medical certificate, an inquest has heard.