BERLIN (AP) — A call from the public was key to foiling an Islamic extremist's plan to use the toxin ricin to carry out a deadly attack in Germany, security officials said Wednesday.

The head of the country's domestic intelligence agency said a phone-in tip helped authorities confirm their suspicions about a 29-year-old Tunisian man in the city of Cologne. The suspect, named only as Sief Allah H. in line with German privacy laws, was arrested last week and remains in custody.

Hans-Georg Maassen, head of the BfV intelligence agency, said the alleged plot showed that the danger of an attack in Germany remains high.

According to federal prosecutors, about 3,150 castor bean seeds and 84.3 milligrams of ricin were found in the suspect's apartment along with the components needed to make a bomb.

Tiny amounts of ricin can kill an adult if eaten, injected or inhaled.

Prosecutors alleged that H. bought the seeds online and used instructions posted online by the Islamic State group to make ricin.

The suspect, who is married to a German woman, allegedly was in contact with Islamic radicals and twice tried to travel to Syria last year, investigators said. They are trying to determine if he was part of a coordinated extremist plot or acted on his own.

German security agencies first were warned about the man by foreign intelligence agencies, but the information provided wasn't conclusive enough to act upon, authorities said.

Holger Muench, the head of Germany's federal police agency BKA, told public broadcaster rbb-Inforadio it wasn't clear if the suspect had picked a specific target to attack.

A Tunisian was behind a truck attack on a Christmas market in Berlin in which 12 people died. The perpetrator was killed in a shootout with Italian police days after the Dec. 19, 2016 attack, which was claimed by the Islamic State group.