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". Sampson joined EOKA and formed part of an execution team under the direct orders of General Georgios Grivas ("Digenis"), leader of EOKA. Another member of this team was Neoptolemos Georgiou who was later arrested for various activities whilst being a member of EOKA-B. Sampson and Georgiou participated in a number of murders carried out along Ledra Street in Nicosia, which was nicknamed "Murder Mile", and shot dead numerous British servicemen, police officers, and civilians. He was involved in at least 15 killings. According to British sources, the actual number was much higher. Among his victims were three police sergeants, and in May 1957, Sampson was tried for one of their murders. He confessed, but was acquitted on the grounds that his confession may have been coerced by torture.