He joined the Lehi at 15 and a half, after being persuaded by one of his uncles, a Beitar member. He assisted in hanging posters in Jerusalem.
In August 1947, his unit, under the command of Amos, set out to hang posters in Bait VeGan. After spotting a British armored vehicle near the bus stop, Amos suggested a change in the plan and offered to go to Edison Cinema instead. Haganah members who were there and knew Shabtai from the neighborhood, probably informed the British of his presence and they arrested him. A British officer put his hand in a bag Shabtai was carrying and without looking at what he pulled out, he claimed: “Sternist!”
Saturn was caught, hiding a dagger and 73 “HaMa’as” posters. In September, he was released on bail. In October 1947, he was acquitted of possession of the dagger. The judge accepted his lawyer’s argument that the dagger was a souvenir and not for use, and also ruled that there was no proof that in Jerusalem it is forbidden to carry a dagger in public.
In November 1947, Shabtai was sentenced in military court to 12 months in prison for carrying 73 Lehi posters on David Yellin Street.
He was held in the Central Prison in Jerusalem, and sat in cell 23 for Lehi members, from November 1947 to February 1948. He was one of the tunnel diggers from which 12 underground men escaped in February 1948. He was then transferred together with other prisoners to the Atlit detention camp.
After his release, he stayed in Lehi’s Ramat Yair base in Sheikh Munis. He participated with other Lehi and Palmach members in the occupation of the Burma Road.
After the independence of Israel, Shabtai worked in the Ministry of Education, in the “Second Chance” program until he retired, providing matriculation exams before recruitment to the IDF for at-risk boys and girls.