Saud al-Qahtani, the former adviser to Saudi Crown Prince Muhammad bin Salman, oversaw the investigation of the arrested activist, Jain al-Hathloul, who was subjected to the most cruel forms of torture and threatened to rape, kill and dump her in the sewers.
Of the 18 women detained, eight were tortured at a government guesthouse in Jeddah before being transferred to a prison, the newspaper said.
According to the same sources, activists Aziza al-Yusuf, Iman al-Najafan and Samar Badawi were among the victims of this torture. Azizah and Eman were also transferred last week from Jeddah to Al-Ha'ir prison in Riyadh, which specializes in criminal offenses.
The Saudi Human Rights Committee, which reports to Saudi King Salman bin Abdul Aziz, has been investigating allegations of torture of several women's rights activists, the paper quoted an official Saudi source and sources familiar with the situation of detained Saudi women activists as saying.
Saudi officials familiar with the matter questioned the investigation leading to criminal charges, saying they did not expect perpetrators to be held accountable for the authorities' failure to acknowledge the torture.
According to the newspaper, the committee began interviews with a number of women activists last month in the prison of Dahban in Jeddah.
Allow access to observers
Human Rights Watch has asked Saudi Arabia to allow international independent monitors access to Saudi human rights activists detained since May to ensure their safety.
The organization said in a statement that on November 28 it had received a report from an "informed source" indicating that a human rights activist had been tortured and that, based on various sources, the torture of female activists may be ongoing.
On November 23 Riyadh denied reports that Saudi activists - including women - had been arrested in a campaign launched by the authorities this year for sexual harassment and torture during interrogation, saying they were "baseless".
Human Rights Watch's call coincided with Reuters's revelation that al-Qahtani personally supervised the torture of an activist and threatened her with rape and murder, while his aides treated and harassed other women.
A group of men tortured the activist and three others with sexual harassment, electrocution and flogging between May and August in an unofficial detention facility in Jeddah, the agency quoted informed sources as saying.