This picture taken on February 24, 2013 shows police investigating by a helicopter in the northern Greece Trikala prison's yard. A helicopter swooped down on a prison courtyard on February 24 as armed men on board fired on guards and lowered a rope to help a convicted killer make his fourth attempt to escape from a Greek prison. But the plot was foiled after the prisoner was shot and the chopper forced to land in the prison's parking lot.