The attack on Rann, home to a camp housing tens of thousands of people displaced by the Islamist insurgency, was one of the group's bloodiest.
“In our recent history, eleven Jews have been assassinated, and some of them tortured, by radical Islamists"
The man, named Amaechi Fred O., was detained on Wednesday in Bavaria.
"Modern day slavery may increase as Daesh struggles to sustain its financial reserves," says researcher.
Amnesty: Boko Haram resurgence kills 381 civilians since April