After managing to escape from Isis, she says she allegedly encountered her tormentor in Germany in 2016 and again in February this year in the southwestern German town of Schwaebisch Gmuend.
"I recognised his face very clearly and whenever I see him I can recognise him ... because of the beatings he gave us," Hami told AP. "We saw him 24 hours a day. So anytime or anywhere I see him, I would be able to identify him."
Hami said she reported the incidents to German police, but — citing fears for her safety — she moved back to Iraq in June.
"I am not ready to sacrifice my honour in Germany," she said. "If I was kidnapped or killed in Germany, who would find out who did that to me?"
Koehler rejected suggestions that German authorities weren't interested in the case.
"If we'd seen an opportunity to arrest someone, we would immediately have done so," she said, noting that German federal prosecutors opened a special investigation several years ago into alleged war crimes committed by Isis militants with the aim of bringing perpetrators to justice.
One of the investigation's elements is the killing of thousands of Yazidis by Isis militants in 2014. Many more were taken into captivity, often kept as sex slaves.
About 3000 Yazidis still remain missing, most thought to have been killed in the war that rolled back Isis control in Syria and Iraq in the last three years.
Jan Ilhan Kizilhan, a German doctor who helped bring hundreds of Yazidi women to Germany in 2015, told public broadcaster ARD yesterday that seeing people who look like their tormentors can sometimes trigger traumatic memories.
Koehler said while the case was difficult, "if we get any further information to firm this up, we will pursue this."
To do so, Hami would need to return to Germany, which she is legally entitled to do, said Koehler.
"Our powers end at the German border," she said.
- AP