As an officer of the Haganah, he served under the leadership of Yitzhak Ben-Zvi, who would in 1952 become the second president of Israel. On June 30, 1924, Tehomi shot and killed Jewish Dutch poet, novelist and diplomat Jacob Israël de Haan, who was living in Jerusalem as a journalist. De Haan had come to Palestine as an ardent zionist, but he had become increasingly critical of the Zionist organizations as he favoured a negotiated solution to the struggle between Jews and Arabs.