On December 21, 1975, six terrorists from the Revolutionary Cells, led by Carlos 'The Jackal' forced their way into the conference room of the OPEC headquarters in Vienna and took seventy ministers hostage. A gun battle with the police ensued, and three people were killed. One terrorist was seriously wounded. The terrorists managed to escape to Algiers with a few hostages and the wounded man. There the hostages were released. The wounded terrorist was Hans-Joachim Klein. At the moment that Klein arrived in Algiers, he decided to quit terrorism.