According to the Swiss paper Tagesanzeiger authorities in Germany and Switzerland are investigating possible links between the 2001 murder of an Israeli-born rabbi in Zurich and a series of murders perpetrated by neo-Nazis.

Rabbi Abraham Grunbaum, 70, was shot and killed on June 7, 2001 in the Agudas Achim synagogue in Switzerland.

According to the JTA news agency the crime was recorded on security camera and police found two bullet casings and cigarette butts at the site. At the time of the 2001 slaying a mentally ill man who was seen leaving the scene at about the time of the attack was arrested but later released, and the case has remained open ever since.

The investigation into Grunbaum’s murder gained new life last week when the terror cell was exposed after two members committed suicide following a failed bank robbery. A third member of the cell then blew up the apartment in which the cell had been living.

She was subsequently arrested and confessed to the group’s involvement in the murders of nine immigrants and a policewoman in Germany over the last decade. A search of the apartment’s remains revealed a “hit list” that included a Jewish member of parliament from Germany.

The revelations led prosecutors in the southern German city of Karlsruhe to order police to explore the possibility the Rabbi – who was not robbed by his killer – was slain by the neo-Nazi cell. They noted the groups murder campaign began in earnest shortly after Grunbaum was slain.

Police recovered the main firearm used in the slayings, which was registered in Switzerland and used at Swiss shooting ranges.

The National Socialist Underground has long been believed to have had connections with Swiss right-wing extremists.

According to the Swiss daily Basler Zeitung, German security forces tapped phone conversations between the two countries verifying the link. Witnesses in Germany have said the group used a vehicle with Swiss plates.

Recent revelations about the National Socialist Underground have spurred calls for banning Germany’s largest right-wing extremist party, the National Democratic Party of Germany, which has some 7,000 members.