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A 30-year-old Tunisian and his 43-year-old German wife have gone on trial on charges they were preparing a biological attack in the name of the Islamic State group.

Sief Allah H. and Yasmin H. are alleged to have produced ricin in their Cologne apartment last year using castor beans purchased online. The bomb was to include steel bearings as shrapnel, with explosives from illegal firecrackers.

Prosecutor Verena Bauer told the court Friday, according to the dpa news agency, that "both defendants identified for a long time with the goal of IS. They planned to detonate a bomb in a crowded place to kill as many unbelievers as possible."

It wasn't clear how potent the ricin they made was. Authorities say a dwarf hamster they tested it on survived.