The Policía de Fronteras seem to have located a vestige of the Nicaraguan civil war. The rusted bayonet and other items were found in or with two backpacks on a farm near the border with Nicaragua.
From the late 1970s until 1987 the border was a war zone as Nicaraguan units sometimes would trespass into Costa Rica, and Costa Rican police were entrenched defending the country.
Police were at first leery of the backpacks for fear they might contain mines. Costa Rica successfully cleared the mines that had been placed along the border, but there could have been others with the find in Cureña de Sarapiquí. The backpacks were partly buried.
Members of the Unidad de Zapadores of the Fuerza Pública, who are experts in explosives, checked out the backpacks and declared them safe.
Some of the items are so rusted that their exact nature is still unknown.