Supreme Leader Ali Khamenei appointed on Thursday former presidential candidate Ebrahim Raisi as head of the Iranian judiciary, taking over from Sadegh Amoli Larijani, who became the chairman of the powerful Expediency Council last December. Raisi had lost to President Hassan Rouhani in the 2017 presidential election. "I am appointing you as the head of the judiciary, as a person who is familiar with the judiciary after years of serving inside the system," Khamenei said in a statement carried by IRNA news agency. Hardline cleric Raisi is a protégé of Khamenei. His appointment is for five years, and could be renewed for a second term. The new head of the judiciary is said to be one of the contestants for the post of Supreme Leader in post-Khamenei Iran. He is known for his role in overseeing the execution of political prisoners in the late 1980s. An audio file release in 2016 proved he was part of a four-person committee that ordered the execution of several thousand political prisoners in 1988. Human Rights Watch said the appointment of a former judge responsible for mass executions to be head of Iran’s judiciary reflects the deteriorating human rights situation in the country. “It’s disturbing and frankly frightening that Ebrahim Raisi will be overseeing justice and accountability in Iran,” said Sarah Leah Whiteson, Middle East and North Africa director at HRW. Khamanei said he appointed Raisi to bring about a transformation in the judiciary, in line with its needs, advancements and challenges on the 40th anniversary of the Revolution.