A suspected Islamic extremist arrested in Cologne succeeded in making ricin and was planning a “biological weapon attack” in Germany, prosecutors said on Thursday.

Sief Allah Hammami, a 29-year-old Tunisian, was held on Wednesday along with his German wife after police found large quantities of the deadly toxin his apartment.

It is believed to be the first time Islamic extremists in Europe have succeeded in manufacturing ricin, which is one of deadliest biological agents known to man.

“This is the biggest potential threat ever found in Europe,” Bild newspaper quoted a source close to the investigation as saying.

Much about the suspected terror plot remains unclear. German authorities say they do not know how advanced the plans were, or what was to be the target of the attack.

Most disturbingly, they say they do not know if the arrested man was working with a larger network.

“We don't know how, or how widely, the ricin was to have been distributed,” Markus Schmitt, a spokesman for prosecutors said.