Taha A.-J. is the husband of Jennifer W., a woman who has been on trial in Munich since last year over accusations that the two mistreated a Yazidi mother and daughter, before allowing the young girl to die.
The case against the couple has been described by media and lawyers as the first time worldwide that an IS member has been tried for crimes against the Yazidis, a religious minority which suffered brutal persecution at the hands of the jihadists from 2014.
Prosecutors allege that A.-J., who joined IS in 2013, purchased the Yazidi child and her mother as household "slaves" and held them captive while living with Jennifer W. in then IS-occupied Mosul, Iraq, in 2015.
Their actions were aimed at "destroying the Yazidis, their religion and their culture in keeping with the aims of IS", the prosecutors' statement said.
The couple are alleged to have forced the mother and daughter to convert to Islam, starved them of food and water and subjected them to beatings.
Read also: Yazidi activist Nadia Murad to use Nobel prize money for Iraqi hospital treating IS victims
A.-J. ultimately chained the five-year-old girl to a window outdoors in heat mounting to 50 degrees Celsius (122 Fahrenheit), leading her to die of thirst.
"The accused thought it possible that the girl would die and recklessly took that into account," prosecutors said.
Arrested in Greece in May 2019 and in detention in Germany since October, A.-J. has also been charged with war crimes, crimes against humanity and human trafficking for labour exploitation.
Jennifer W. has been on trial in Munich since April.
Recruited to IS in mid-2015, she was later arrested in Turkey and extradited back to Germany, but not convicted.
She was arrested again in June 2018 after speaking about the Yazidi child's death to an undercover police informant, who she believed would help her return to IS territory.
Prominent London-based human rights lawyer Amal Clooney is part of the team representing the dead Yazidi girl's mother, who is a co-plaintiff in the case.
Clooney, the wife of Hollywood star George Clooney, has been involved in a campaign with Nobel Peace Prize winner Nadia Murad, a former IS sex slave, to have the IS crimes against the Yazidi minority be recognised as a genocide.
Follow us on Twitter and Instagram to stay connected