Zaur Dadayev allegedly confessed and was charged but has now insisted to the council's Andrei Babushkin that he is "innocent" and only made the admission under duress.
"There are reasons that lead us to believe Zaur Dadayev confessed under torture," Babushkin told AFP after a visit to the suspect's Moscow prison cell yesterday.
"We cannot confirm that he was tortured as we are not investigators but we did find numerous wounds on his body," said Babushkin, who was swiftly rapped over the knuckles by investigators for meddling in their probe.
Dadayev, a former deputy commander in a special Chechen police unit, was charged by a Moscow court on Sunday with the murder alongside Anzor Gubashev who worked for a private security company. The two men and three other suspects were remanded in custody.
Also Read
A court in Moscow heard the men were being probed under a section of the Russian criminal code relating to murders carried out for financial gain, in a sign investigators believe Nemtsov's murder was a hit.
"They shouted at me all the time, 'You killed Nemtsov, didn't you?'. I said, 'no'," Babushkin reported Dadayev as saying.
The suspect said he had eventually admitted to the killing to secure the release of an ex-colleague, Ruslan Yusupov, who was detained alongside him.
"They said that if I confessed they would let him go. I agreed. I thought I would save him and they would bring me to Moscow alive," Dadayev was quoted as saying by Babushkin.
Russia's powerful investigative committee condemned Babushkin's statement as breaking the law and said that he and a colleague who visited Dadayev would be questioned over possible "interference in a criminal case".