Harvey Nichols killer Michal Pech used to work as a security guard at the US embassy in the Slovakian capital Bratislava, a former employer has said.
Pech turned the gun on himself after shooting Miss Bernal
Czech-born Pech, 30, who protected US diplomats and staff at the embassy, received weapons training during his national service, said Michal Duha.
Pech shot dead his former lover Clare Bernal at the exclusive London store before killing himself on Tuesday.
"It is shocking to believe our friend could have done this," said Mr Duha.
"He was such a quiet man and so friendly, he always kept a smile on his face and was happy, absolutely great to work with.
"There were never any problems with him, he was a friend and at one time I was going to promote him because he was doing a good job, but he decided to leave."
Speaking from Bratislava, Mr Duha, who employed Pech at Group 4 Falck - a subsidiary of Group 4 Securicor - said he left for the UK in 2003.
He described Pech as a "quiet man" and a keen fitness enthusiast, who had never displayed "violent or aggressive behaviour towards anyone".
"He had a girlfriend at the time and was happy with her, we never heard of any trouble between them," he said.
Pech, who lived in a shared house in Tottenham, north London, left his job at Harvey Nichols in December.
He began stalking Miss Bernal, 22, from Tunbridge Wells after they broke up earlier this year, and had threatened to kill her.
He had recently pleaded guilty to harassing her and was banned under a court order from approaching her.
While he was out on bail, he travelled to the department store and used a German-made Luger pistol to shoot Miss Bernal.