MOSCOW, April 2. /TASS/. Russian opposition activist Ildar Dadin, who was detained on Sunday for a one-man picket in front of the building of the Russian interior ministry’s Moscow department, has been released, his wife, Anastasia Zotova, told TASS.

"Ildar has just been released," she said.

After detention, Dadin was taken to the Tverskoy police station to be questioned as a witness in the criminal case over calls for mass riots that was opened against unidentified persons.

On March 10, Dadin was detained at the building of the Federal Penitentiary Service in central Moscow after he had refused to show his passport. Dadin’s wife, Anastasia Zotova, said he had left his passport at home. The activist took part in a picket, along with human rights activist Lev Ponomarev, demanding resignation of a number of penitentiary system officials, including the chief of the Karelia colony.

In December 2015, Moscow’s Basmanny District Court found Dadin guilty on four counts of participating in unauthorized protests in Moscow. He was sentenced to three years in a penal colony but then the Moscow City Court reduced his jail term to two and a half years. On February 10, 2017, Russia’s Constitutional Court ruled to review Dadin’s case which was done by the Supreme Court on February 22. The Supreme Court ruled to cancel Dadin’s conviction and release the activist.

In November 2016, the Russian media published a letter by Dadin saying that he was subject to torture while serving his sentence in the Segezh colony in Karelia, northwestern Russia. However, independent doctors who visited him in the colony found no signs of bodily injuries, neither did investigators. Later it became known that after a probe, Dadin was transferred to a penal colony in the Altai region, Siberia.