A man linked by officials to the attack on the U.S. consulate in Benghazi has been conditionally released by a Tunisian judge, an adviser to Tunisia's justice minister said Tuesday.

The adviser, Kamel Ben-Jaballah, told NBC News that Ali Harzi, 26, was released from custody by the investigative judge yesterday.

Harzi, however, remains "technically under investigation" and his release is "temporary," Ben-Jaballah said, adding that Harzi is subject to a travel ban that forbids him from leaving greater Tunis.

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Harzi's lawyer said that his client, who is Tunisian, was released for lack of evidence.

Harzi's release appears to be a setback to the investigation of the Sept. 11 attack on the consulate that killed four Americans, including Ambassador Christopher Stevens, information management officer Sean Smith and security personnel Tyrone Woods and Glen Doherty.

The investigation in Libya has been stalled due to the weak central government in the face of the powerful militias, some of which may have been involved in the attack.

Harzi was one of very few people in custody in relation to the attack. U.S. officials told NBC News in December that Egypt had also arrested a member of the group Islamic Jihad for possible links to the attack, but in general they lamented a lack of cooperation from local governments in their investigation and said most suspects remained free.

The attack became a political bombshell in the United States, with critics of President Barack Obama's administration saying that more should have been done to protect the embassy, particularly after officials had requested extra security.

A scathing report cited "systemic failures" within the State Department and was at least partially responsible for the resignation of the assistant secretary of state for the Bureau of Diplomatic Security. Three other officials were relieved from duty after the report was released.

Harzi's lawyer, Anwar Oued-Ali, said the presiding judge had "conditionally freed" his client Monday night and that he must remain nearby in case he is needed. The lawyer described the release as "correcting an irregular situation" because, he claimed, authorities never had any real evidence.

Benghazi coverage from NBC News

Harzi was originally detained in Turkey, and in October was extradited to Tunisia, where authorities had said he was "strongly suspected" of being involved in the attack. His lawyer said he was officially charged with "membership of a terrorist organization," a charge punishable by six to 12 years in prison.

In December, FBI officials questioned Harzi for three hours in the presence of a Tunisian judge.

The Associated Press contributed to this report.

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