Alexander was born in Jerusalem on October 17,1929, to Yehoshua Yedidya and Miriam. His father was a pharmacist in Me’ah She’arim. As a child, Alexander was affectionately called Sanny. He attended the Tahkemoni School, then the B’Maaleh School. He was full of life and very sociable, but also serious, modest, and gentle.

As a high-schooler, Alexander joined Brit Hashmona’im and, in 1946, Lehi. The principal of his school found out and expelled him, as per the rules set by the National Institutions at the time. Alexander continued his studies on his own and prepared to take external matriculation exams. But all the while, most of his energies were devoted to the underground. Soon, he was appointed to supervise a cell of youths who distributed propaganda literature and hung wall-posters.

On May 6, 1947, Alexander told his parents he was going to pick up some study materials from a friend, but instead went to meet up with his underground comrades. He was never seen again. When he failed to return home, his family published his photograph and asked the public to help find him. A thirteen-year-old student told them he saw Alexander being chased and forcibly put into a car, which sped off.

During the abduction, a hat had fallen off one of the men who pursued Alexander.  The name in the hat indicated it belonged to Major Roy Farran. Farran commanded a secret British undercover unit that combated the Jewish undergrounds using “dirty” methods. He fled to Syria but public pressure forced the British to return him to Eretz Israel; when he was finally put on trial, he was acquitted. Farran returned to Britain a respected man.

Alexander’s body was never found; a stone stands in his memory on Mt. Herzl in Jerusalem, in the section for soldiers who are missing in action. Students of the Rabbi Pardes School also planted a forest in his name, a street in the Talpiot neighborhood of Jerusalem bears his name, and the Jerusalem Municipality put up a plaque on Ussishkin Street, near the site of his abduction.

Alexander knew of weapons caches, meeting places and the names of many underground members. The fact that the British did not find any of these means that Alexander withstood Farran’s torture, preferring to die rather than betray his Lehi comrades.