Prosecutor: Iowa teens killed Spanish teacher over bad gradeDES MOINES, Iowa (AP) — Two Iowa teenagers killed their high school Spanish teacher last year because of frustration over a bad grade, prosecutors said Tuesday in court documents that for the first time reveal a possible motive.Graber later drove her van to a park where she was known to take daily walks after school, authorities say.Paris court to deliver verdict in trial of Liberian ex-rebelTennessee man gets 40 years for shooting federal officersAustralian inquiry probes 40 years of gay hate killingsConnecticut governor candidates clash over police deathsThe van was left at the end of a rural road.Miller initially denied any involvement in Graber’s disappearance but “later stated he had knowledge of everything but did not participate,” according to court documents.He told police that the real killers — a “roving group of masked kids” — forced him to provide his wheelbarrow to help move her body and to drive her van from the park."