During the Cyprus Emergency, in which the EOKA guerrilla group waged a campaign of resistance to British colonial rule in Cyprus from 1955 to 1959, Sampson joined EOKA and adopted the nom de guerre Atrotos (), or "Invulnerable".
At the time, Sampson was working as a journalist, and he would often photograph the bodies of his victims after killing them, then send the photographs to The Cyprus Times newspaper to be published.