A German convert to Islam who was investigated in connection with the April bombing of a synagogue in Tunisia left Germany last month, German prosecutors said today. According to a German television news report, the man went to Saudi Arabia and police learned of his departure only after the fact.

Christian Ganczarski, 35, was a well-known activist in radical Islamic circles in the western city of Duisburg. According to German officials, he received a call from the driver of a truck laden with heating gas shortly before the truck exploded at a historic synagogue in Djerba, Tunisia, killing the driver and 19 other people, including 14 German tourists.

During the call, which was intercepted by German intelligence, the driver, Nizar Naouar, was asked by Ganczarski if he needed anything and replied, "I only need the command," German officials have said.

German police briefly detained and questioned Ganczarski after the bombing, but released him without charge, citing a lack of sufficient evidence to go to trial.

In a statement this evening, the German prosecutor's office said Ganczarski and his family were allowed to leave the country last month. "Since the suspicion was not sufficiently strong for an arrest warrant to be issued, the justice authorities did not have the possibility to prevent the suspect leaving the country," the statement read.

The German television station ARD reported tonight that Ganczarski, who was supposed to be under surveillance, was out of the country before police realized he had left. The station reported that he flew to Saudi Arabia from Amsterdam via Frankfurt. Officials declined to comment on that report.

Police raided Ganczarski's home after the Tunisia bombing and found the telephone number of Mounir Motassadeq, an alleged back-office fixer for the al Qaeda terrorist cell in Hamburg that led the Sept. 11, 2001, attacks in the United States. Motassadeq is on trial in Hamburg on more than 3,000 counts of accessory to murder.

According to another terror suspect who gave testimony at the trial, Ganczarski had contact with the leadership of the al Qaeda network and may have recruited in Germany for the organization. The witness, Shadi Abdallah, told police that Ganczarski had trained at military camps in Afghanistan.

Ganczarski also was an acquaintance of Mouhamedou Ould Slahi, a former resident of Duisburg who was turned over to the United States by the government of Mauritania after Sept. 11 on suspicion of involvement in a plot to bomb Los Angeles International Airport during the 2000 millennium celebrations, according to intelligence sources.