Kenyatta's imprisonment transformed him into a political martyr for many Kenyans, further enhancing his status. A Luo anti-colonial activist, Jaramogi Oginga Odinga, was the first to publicly call for Kenyatta's release, an issue that gained growing support among Kenya's anti-colonialists. In 1955, the British writer Montagu Slater—a socialist sympathetic to Kenyatta's plight—released "The Trial of Jomo Kenyatta", a book which raised the profile of the case. In 1958, Rawson Macharia, the key witness in the state's prosecution of Kenyatta, signed an affidavit swearing that his evidence against Kenyatta had been false; this was widely publicised. By the late 1950s, the imprisoned Kenyatta had become a symbol of African nationalism across the continent.