The boyfriend of a University of Iowa student testified Wednesday that he had nothing to do with her 2018 abduction and stabbing death, saying he had been out of town for work and was heartbroken by her slaying, and he “wholeheartedly” believes the suspect is guilty. Dalton Jack, the longtime boyfriend of Mollie Tibbetts, was a key witness on the first day of the first-degree murder trial of Cristhian Bahena Rivera, an illegal immigrant charged in her killing. Prosecutor Bart Klaver said in his opening statement Wednesday that video evidence, DNA analysis and a partial confession by Rivera, a dairy farm worker, will be crucial to proving his guilt. Tibbetts, 20, disappeared while out for a run in Brooklyn, Iowa, on July 18, 2018. Her body was recovered a month later in a cornfield. During cross-examination, defense lawyers for Rivera worked to try to cast suspicion on Jack, painting him …