Libya’s Chief of Judicial Police, Osama “Al Masri” Njeem, returned to Libya on an Italian government plane after his arrest in Italy on January 19 on an International Criminal Court (ICC) warrant.

His release two days later was for what the Italian government said on Wednesday were “inaccuracies” in the warrant.

Njeem is accused by the ICC of crimes committed in his role overseeing the Tripoli branch of the Reform and Rehabilitation Institution, a network of detention centres run by the government-backed Special Defence Force (SDF).

Amnesty International identifies Njeem as a “long-term member of Tripoli-based militia the Deterrence Apparatus for Combatting Terrorism and Organised Crime (DACTO)”, one of several militias the internationally recognised Tripoli government relies on, and absorbs, to project power across the western parts of Libya, which it nominally controls.

The rights group “has long documented horrific violations committed with total impunity at the Mitiga prison in Tripoli, under the control of DACTO”, and says there is “no prospect of domestic accountability in Libya of powerful commanders of militias”.

Al Jazeera has spoken to two people who were held in prisons overseen by Njeem about the atrocities they witnessed.

“I saw him commit war crimes. I saw him kill people,” David Yambio, president of the NGO Refugees in Libya, said.

The accusations against Njeem are numerous, ranging from murder to torture and people trafficking.

His release has been condemned as “outrageous” by rights groups and “hypocritical” by leading political figures within Italy. Shortly after Njeem was returned to Libya, Italian Interior Minister Matteo Piantedosi told the Italian senate he had been released, rather than handed over to prosecutors from the ICC, “in view of the danger [he] posed [to Italian society]”. A little more than a week later, the justice minister announced that the release had been on a legal technicality.

Njeem is said by the ICC to control several prison facilities in Tripoli, including that at Mitiga, Ain Zara and al-Jadida, “where thousands of persons were detained for prolonged periods”.