Anzor Gubashev, charged with involvement in the murder of Russian opposition figure Boris Nemtsov, hides his face as he sits inside a defendants' cage in a court building in Moscow, March 8, 2015. Reuters/Tatyana Makeyeva

The suspect who confessed to killing Russian opposition leader Boris Nemtsov is a decorated former Chechen police officer who was deeply offended by depictions of the Prophet Muhammad in French satirical magazine Charlie Hebdo, Chechen leader Ramzan Kadyrov said Sunday. Remarks on Kadyrov's Instagram account appeared to give credence to theories the killing within sight of the Kremlin was the work of Islamists, Reuters reported.

Zaur Dadaev appeared in court Sunday with four other suspects. He was the only one to plead guilty. A sixth suspect blew himself up with a grenade in Grozny, Chechnya, late Saturday as police tried to arrest him, Interfax reported. Reuters said before killing himself, the suspect lobbed a grenade at police.

Russian officials have denied complicity in Nemtsov's killing, even though some of Nemtsov's associates have said the Kremlin stands to gain from his death.

Nemtsov, 55, a former deputy prime minister and among the government's most persistent critics, was shot to death near the Kremlin Feb. 27 just before he reportedly planned to outline Russian military involvement in Ukraine -- something the Kremlin has denied, asserting any Russians fighting in Ukraine are volunteers. Nemtsov and his girlfriend were walking across a bridge over the Moscow River when he was shot in the back. She was uninjured.

Kadyrov described Dadaev as "a true patriot of Russia," who had several medals for bravery, and a devout Muslim. He said it was unclear why Dadaev resigned from his interior ministry regiment.

"All who know Zaur [Dadaev] confirm that he is a deep believer and also that he, like all Muslims, was shocked by the activities of Charlie [Hebdo] and comments in support of printing the cartoons," Kadyrov wrote on his Instagram account.

"Dadaev's involvement in committing this crime is confirmed by, apart from his own confession, the totality of evidence gathered as part of this criminal case," Judge Natalia Mushnikova said in ordering Dadaev and his alleged accomplices held through April 28.

The other suspects were identified as brothers Anzar and Shagid Gubashev, Ramzan Bakhaev and Tamerlan Eskerkhanov, ITAR-Tass reported.

Shagid Gubashev denied involvement during the hearing in Basmanny District Court, saying he has witnesses to prove he was elsewhere. "I did not commit this crime. I have health problems -- ulcers and hemorrhoids," he said, adding he learned about the shooting from the media.

Eskerkhanov, Bakhaev and the Gubashev brothers all pleaded not guilty despite evidence police said indicates otherwise, RIA Novosti reported.