A guard at a northern Greek prison was arrested yesterday on suspicion of regularly smuggling drugs into the penitentiary for the use of inmates. The 38-year-old man, whose name was not made public, allegedly cooperated with two former prisoners in providing convicts at the Diavata prison, near Thessaloniki, with parcels of heroin. The drugs were left at night in a prison garbage can, from where convicts collected them in the morning. But the system broke down late last month when other guards found 82 grams of heroin in the can, prompting higher vigilance for smugglers. The guard aroused suspicion shortly afterward when he asked a colleague to switch shifts so that he would be on night duty. Officers found 155 grams of heroin in the suspect’s possession at the time of his arrest. Police are now investigating whether he was also involved in smuggling in a batch of firearms seized in the prison five months ago.