Castro resigned last month amid criticism of his handling of sexual assault allegations against a top Fresno State administrator while he was president of the university.
The investigation will focus on how the university responded to six years' worth of sexual misconduct complaints.
The majority of those claims - which were made between 2014 and 2019 - involved Frank Lamas, the former Vice President of Student Affairs at Fresno State.
"It is important that we understand how campus leaders at Fresno State responded to the workplace concerns about Dr. Frank Lamas," stated CSU Board of Trustees Chair Lillian Kimbell. "We will investigate the past to reveal potential new facts, learn and take appropriate action."
The CSU system has hired Cozen O'Connor, an international law firm, to handle reviews of Title IX policies and practices at all 23 CSU campuses.
Fresno State will be the first university the law firm investigates. Last month, a USA Today report exposed the misconduct claims against Lamas.
In his resignation statement, Castro said he disagreed with media reports, but found it necessary to resign in order for the CSU system to maintain its focus on education.
CSU has also revised its practices regarding the ability for an administrator to retreat to a faculty position.
"Retreat rights are very important and valuable to our community," stated acting Chancellor Relyea. "That opportunity to retreat should be extended to individuals in good standing with the CSU, not to individuals who have engaged in significant misconduct. The policy needs systemwide clarity, consistency, and modernization, thus we are reforming it."
The new policy will prohibit an administrator's return to the faculty under certain circumstances, including allegations of sexual harassment or other misconduct.
"The safety and well-being of our campus communities continues to be the highest priority for the CSU," read a statement issued by the school. "Reports, concerns or questions about sexual harassment or other sexual discrimination should be directed to a campus Title IX Coordinator or the Office of Systemwide TIX Compliance."