Five people have been detained in connection with Nemtsov's shooting on Feb. 27. Zaur Dadaev was the only one who, according to a judge and investigators, confessed to the killing.
Russian news agencies on Wednesday quoted Dadaev as telling the court that he had been abducted, beaten and pressured to confess to the shooting.
"I was kidnapped by unknown men on March 5," he said in comments carried by the Interfax news agency. "I don't know where I was being kept, but the formal arrest at the Investigative Committee did not happen until March 7."
Dadaev said that before he was arrested he was "told what to say and how to say it."
At a court hearing in March, Dadaev didn't admit guilt in the courtroom and later retracted his confession given to investigators while a human rights activist who visited Dadaev in jail last month talked about signs of torture on Dadaev's body.
Dadaev's lawyer, Ivan Gerasimov, said after the hearing that his client didn't even know who Nemtsov was before he was arrested.
All five suspects are from Chechnya in the North Caucasus. Their origin raises a potentially sensitive issue, given the significant animosity for Caucasus groups among ethnic Russians.
Dadaev had been an officer in the Chechen police troops.
Nemtsov's killing just outside the Kremlin's walls shocked Russia's already beleaguered opposition supporters. Many of Nemtsov's allies and colleagues are skeptical about the Chechen theory, arguing that Nemtsov's death in a tightly secured area near the Kremlin wouldn't have been possible without official involvement.
The Moscow City Court on Wednesday extended the arrest for Dadaev for another month.
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