DES MOINES, Iowa—A judge on Monday rejected a convicted illegal immigrant’s request for a new trial in the 2018 killing of University of Iowa student Mollie Tibbetts, whose body was found in a cornfield weeks after she disappeared while out for a run near her small hometown. Judge Joel Yates’ ruling cleared the way for sentencing to proceed Aug. 30 in the trial of Cristhian Bahena Rivera, who was convicted in May of first-degree murder in Tibbetts’ death. The former farmhand, who came to the United States illegally as a teenager, faces a sentence of life in prison. Yates rejected efforts by Bahena Rivera’s attorneys to implicate others, saying much of the evidence they presented after he was convicted was known to them before the verdict was handed down. To grant a new trial, any additional evidence would have to be new and revealed after the verdict, he wrote. The …