Russia's top investigative body on Tuesday said it would charge five men in connection to the February assassination of Kremlin opposition leader and former deputy prime minister Boris Nemtsov, who was an outspoken critic of President Vladimir Putin.

Nemtsov, who was working on a report detailing Russian military support for rebels in eastern Ukraine, was shot as he strolled across a bridge some 300 feet from the Kremlin with his girlfriend.

Nine days after the murder, amid fevered speculation about who ordered the hit and why, Zaur Dadayev, a dismissed deputy commander of an interior ministry battalion in the Russian republic of Chechnya, was detained and soon confessed to having fired the four bullets that killed Nemtsov. He later recanted his confession, which he said was given under duress.

The other four suspects being charged in the killing are also natives of Russia's restive Chechnya republic — among them Ruslan Mukhudinov, a former officer in Chechnya's Interior Ministry who remains at large. Though long said to have helped organize the murder, Russian authorities on Tuesday named him as the mastermind.

Mukhudinov's lawyer has argued that there is no solid evidence against him. Vadim Prokhorov, a lawyer for the Nemtsov family, said the idea that Mukhudinov was the mastermind was "complete nonsense" and looked like a bad joke.

"That he is one of the low-level organizers is obvious," said Prokhorov. "But the masterminds are highly-placed people."

ZhannaNemtsova, Nemtsov's daughter, said she was disappointed with the investigation. She has previously said she wants Ramzan Kadyrov, the Kremlin-backed head of Chechnya, to be questioned about the case.

Mukhudinov once worked as a driver for an associate of Kadyrov's in a Chechen military battalion. Kadyrov, who praised the devotion to Russia of Dadayev, the suspected gunman, after his arrest, has denied any involvement in the Nemtsov murder.

"Let her look for who organized the murder in his circle and not accuse me," Kadyrov remarked a Russian radio station in October. "I am... a suspect if you listen to some liberal devils who accuse me of killingNemtsov. It's total nonsense."

Zaur Dadayev sits in a cage inside the Basmanny City Court in Moscow, Russia, April 23, 2015. (Photo by Maxim Shipenkov/EPA)

According to a security official in Ingushetia, a region neighboring Chechnya where some of the suspects were detained, Dadayev served for 10 years in the Sever Interior Ministry battalion in Chechnya.

The Sever battalion is led by the brother of Adam Delimkhanov, a member of the Russian Duma and a close ally of Kadyrov.

In March, anti-corruption campaigner Alexei Navalny wrote in a blog post that the murder could have been carried out by some of the many security personnel in the employ of Kadyrov, who is known for his support of Vladimir Putin and criticism of Russia's political opposition. Kadyrov told thousands of his heavily-armed men assembled at a stadium in December that "we are the foot soldiers of Vladimir Putin," declaring his loyalty to the Russian president.

While Kadyrov put down an anti-Moscow insurgency in Chechnya, helping Putin cement his rule, he also represents a risk for the Russian leader.

Putin gave Kadyrov a large degree of autonomy to run his region as he chooses, which has largely worked for both men, but some observers say Kadyrov is overstepping the mark. Russian media have reported incidents of police in Moscow having run-ins with Chechens, then coming under pressure not to prosecute them because of their ties to Kadyrov.

Russian officials have denied involvement in Nemtsov's death and Putin called the killing a shameful tragedy.

Russia's Investigative Committee said in a statement that it expects to apprehend Mukhudinov shortly, according to the Associated Press, and noted that the formal probe into Nemtsov's death is expected to finish in January.

Russian courts have sentenced shooters in other high profile political murders like that of journalist Anna Politkovskaya in 2006, but critics say that those convicted of past assassinations were the patsies of larger conspiracies, scapegoated in order to silence critics and weaken Russia's opposition.