BELGRADE, Serbia (AP) — Authorities in Serbia have displayed stacks of guns and cartons of hand grenades from the thousands of weapons they say people have handed over since back-to-back mass shootings stunned the Balkan nation. The government declared a one-month amnesty period for citizens to surrender unregistered weapons following the two shootings in two days this month that left 17 people dead, many of them children. President Aleksandar Vucic accompanied police officials to view the assortment of arms on Sunday. Officials said residents had turned over about 13,500 items since the amnesty opened, including anti-tank rocket launchers. Photos from the scene showed lines of rifles, automatic weapons and pistols stacked neatly on the floor in a warehouse.