Saudi authorities have released Matrouk al-Faleh, a political scientist and one of Saudi Arabia’s leading human-rights activists, after holding him without charge for nearly eight months, CNN reports.

It remains unclear why Mr. al-Faleh was released or even why the Saudi secret police arrested him in the first place, on May 19 in his office at Riyadh’s King Saud University.

The arrest came shortly after Mr. al-Faleh publicly criticized the harsh and overcrowded conditions that two of his clients were facing in prison. Both men were fellow human-rights activists who had been found guilty of “incitement to protest” after supporting a demonstration outside the prison.

The American Political Science Association, Amnesty International, and Human Rights Watch were among the groups that appealed to Saudi authorities for Mr. al-Faleh’s release. Many activists were concerned that he could face torture and other ill treatment while in prison, especially since his family members were not allowed to contact him and were not even told of his condition.

It is unclear what conditions Mr. al-Faleh faced while he was locked up in the Al-Hayer maximum-security prison, near Riyadh. However, Mr. al-Faleh was reported to be in good health when he was released late Saturday.

“He is very healthy, and his morale is quite high — surprisingly after eight months,” Mohammed al-Qahtani, a colleague, told CNN after he visited with Mr. al-Faleh at home on Sunday. —Andrew Mills