Castro took a redshirted season in 2019.[3] In the 2021 season, he recorded six tackles in four games.[4] In 2022, Castro notched 33 tackles, a sack, five pass deflections, and a pair of forced fumbles.[5] In week two of the 2023 season, he had four tackles and his first career interception, which he returned 30 yards for a touchdown, as helped the Hawkeyes beat rival Iowa State.[6] For his performance, Castro was named the Big Ten Conference defensive player of the week.[7] In week seven, he tallied seven tackles with two going for a loss, a pass deflection, and the game sealing interception, as he helped Iowa beat Wisconsin.[8] For his start to the season, Castro was named a second-team midseason All-American by the Associated Press.[9]