Berlin police said they were investigating "in all directions" Wednesday after a man attending a public lecture fatally stabbed Fritz von Weizsäcker, a son of the late Richard von Weizsäcker — the West German president and then German president between 1984 and 1994.

Fritz von Weizsäcker was stabbed to death on Tuesday evening while giving a lecture attended by some 20 people at the Schlosspark hospital in the western Berlin neighborhood of Charlottenburg, where von Weizsäcker is a senior internal medicine specialist.

Police apprehended the attacker with the help of members of the crowd. The 57-year-old suspect was "previously unknown" to authorities, said police, suggesting he had no prior criminal record.

The suspect was sent to a psychiatric unit later on Wednesday, described as having an "acute psychological illness."

One other person, an off-duty police officer in the audience, was also seriously injured while trying to stop the attacker. The officer was taken to a different hospital to receive treatment, Berlin's fire department said on Twitter.

The Schlosspark hospital regularly holds events that are open to members of the public. The private clinic includes departments for gastroenterology, cardiology, orthopedics, plastic surgery, neurology and psychiatry.

A murder investigation has been opened and investigators were at the scene taking statements from audience members and employees, authorities said.

Read more: Opinion: The speech about history that made history

People attending von Weizsäcker's talk were able to apprehend a suspect in the stabbing

'Stunned' by killing

Chancellor Angela Merkel expressed her condolences to Fritz von Weizsäcker's widow, her spokesman said.

"We don't know much about what happened here in Berlin last night,'' spokesman Steffen Seibert said in Berlin. "It's a horrible blow to the von Weizsäcker family and the chancellor's condolences, and certainly also those of all the members of the government, go to the widow, to the entire family.''

Christian Lindner, the leader of Germany's Free Democratic Party, said he was "stunned" by the killing.

"My friend Fritz von Weizsäcker was stabbed today in Berlin. A passionate doctor and a fine person," Lindner wrote. "He was just over at our house for a barbecue. I am stunned and must share my sadness. Once more you ask yourself, in what world do we live."

Von Weizsäcker had a long career in medicine. He studied in Bonn and Heidelberg, followed by career steps in Freiburg in southern Germany, Boston and Zurich, according to Schlosspark's website.

His sister Beatrice von Weizsäcker, a lawyer and journalist, posted a picture of Jesus on the Cross on Instagram after the murder of her brother.

Fritz von Weizsäcker was one of four children of Richard von Weizsäcker, a veteran of Germany's Christian Democrats, now headed in a grand coalition cabinet by Chancellor Angela Merkel; Richard von Weizsacker served as German president from 1984 to 1994 and passed away in 2015.

Berlin's mayor between 1981 and 1984 — during Germany's Cold War division — Richard von Weizsäcker oversaw the fall of the Berlin Wall and German reunification as federal president. He was also a prominent synodic member of Germany's EKD Protestant Church in the 1960s and 70s.

In 1985, then as West German president, von Weizsäcker called the Nazi defeat Germany's "day of liberation" in a speech marking the 40th anniversary of World War Two's end.

His speech is often cited by politicians and taught in schools.

A wise and respected voice An outstanding politician He was born in a palace in Stuttgart and would become both the governor of Berlin and the sixth president of the Federal Republic of Germany. Richard von Weizsäcker, who belonged to the Christian Democratic Union, was known as a moral authority in Germany.

A wise and respected voice Fraught family ties His father, Ernst von Weizsäcker, was a senior figure in Hitler's NSDAP. After the Second World War, he was sentenced to seven years in prison for war crimes. He was convicted for complicity in the deportation of Jews, a sentence that would influence the life of his son, Richard von Weizsäcker.

A wise and respected voice Early political life He married his wife Marianne Weizsäcker, with whom he had four children, in 1953. After studying law, he worked in a number of leading companies in Germany, among them Boehringer Ingelheim. Von Weizsäcker joined the CDU in 1954. Helmut Kohl discovered him early and recommended him for the office of president in 1968 - without success.

A wise and respected voice A respected mayor In 1982, as governor of Berlin, he received - together with then Chancellor Helmut Schmidt - the president of the United States, Ronald Reagan. He was able to push through a number of reforms during his tenure in Berlin, including the creation of an immigration representative.

A wise and respected voice Bridging the divide On September 15, 1983, von Weizsäcker was received by the head of East Germany, Erich Honecker, in East Berlin. This was the first meeting of its kind, and it was an important symbol of reconciliation between East and West Germany. This was one reason why von Weizsäcker was named honorary citizen of the German capital following reunification, in 1990.

A wise and respected voice A respected statesman On July 1, 1984, von Weizsäcker was voted almost unanimously as president of Germany. From then on, he was seen as a high representative of the republic and respected for his humor and the way in which he represented Germany as head of state.

A wise and respected voice Words that live on "May 8, 1945 was a day of liberation." Richard von Weizsäcker made his observation about the end of the Second World War during a commemoration ceremony in 1985. He received both praise and criticism for speaking those words - and went down in history.

A wise and respected voice On the periphery During his tenure as president, the reunification of West and East Germany took place. Helmut Kohl will forever be known as the "Chancellor of Re-Unity," though von Weizsäcker remained on the fringe. He preferred not to overemphasize the convergence of the German two states.

A wise and respected voice Campaign for Europe Even after his tenure, von Weizsäcker remained active on a political level. Before the eventual implementation of the euro in 2001, he could be seen as a campaigner for the European currency, a sign of his desire for a unified Europe - or at least a monetary European Union. Author: Jeanette Seiffert / gb



ipj, dv/sms (AFP, dpa)

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