ALEXEI Navalny was killed with one punch to the heart after being forced to spend hours in freezing temperatures, it has been claimed.
The brutal method was once a "hallmark of the KGB", according to the founder of human rights group Gulagu.net.
Vladimir Putin's most formidable domestic opponent Navalny, 47, died in prison on Friday while serving a 19-year sentence on extremism charges at the IK-3 Arctic prison colony.
Russia claimed the lawyer died of "sudden death syndrome".
It was later alleged that his body had been found covered in bruises, as his spokeswoman Kira Yarmysh asserted he was "murdered".
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Russian-born human rights activist Vladimir Osechkin told The Times that the bruising found on Navalny's body was consistent with the "one-punch" technique previously taught to KGB special forces operatives.
Osechkin further claimed that the Russian lawyer was forced to spend more than two and a half hours outdoors in an open-air solitary confinement space where temperatures were as low as -27C.
Prisoners were normally kept outside for no more than an hour - much less in such extreme conditions.
The Russian dissident's information was said to have come from a source working in corrective colony FKU IK-3 - also known as the Polar Wolf jail - where Navalny died.
He said: "I think that they first destroyed his body by keeping him out in the cold for a long time and slowing the blood circulation down to a minimum.
"And then it becomes very easy to kill someone, within seconds, if the operative has some experience in this.
"It is an old method of the KGB’s special forces divisions. They trained their operatives to kill a man with one punch in the heart, in the centre of the body. It was a hallmark of the KGB."
Former prisoners who have served sentences in the Arctic region previously reported that inmates were killed by their jailers in the same way, Osechkin added.
Russia’s Federal Penitentiary Service initially said that the Putin critic had "felt unwell" after taking a walk in the prison, "almost immediately losing consciousness", and that medical staff were unable to save him.
A state-controlled channel on Telegram claimed the same day that he had died of a blood clot.
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On Saturday, Navalny's mother and his lawyer were informed he had died of "sudden death syndrome".
Navalny's heartbroken widow Yulia Navalnaya suggested on Monday that he was killed using novichok, the nerve agent which FSB assassins used in their attempt to kill him in August 2020.
Speaking on the possibility of the poison being Navalny's cause of death, Osechkin said: "It’s possible of course, but when someone is under the control of the prison system there are many options as to how to kill them.
"Novichok would leave a trace in his body and would lead directly back to Putin, given he has tried it once before."
Based on information provided to him by his sources, he said he believed that Navalny's death was "a special operation that had been prepared several days in advance".
Osechkin claimed: "It was a command from Moscow because without Moscow it would not have been possible to dismantle the cameras in the way that they did."
Navalny's mother Lyudmila, 69, made an emotional address to Putin on Tuesday from outside the jail where her son died, calling on the president to release his body to allow for a humane burial.
She said: "Behind me is the penal colony IK-3 Polar Wolf, where my son Alexei Navalny died on February 16.
"For the fifth day I cannot see him. They don’t give me his body and they don’t even tell me where he is.
"I appeal to you, Vladimir Putin, the solution to the issue depends only on you. Let me finally see my son.
"I demand that Alexei’s body be immediately handed over so that I can bury him humanely."
Reports later emerged that Putin allegedly had his sights set on her other son, Oleg.
It was claimed Navalny's younger brother, a 40-year-old dad of two, was facing a new and unspecified criminal charge in Russia.
He is currently believed to be abroad and has been seen in Cyprus and Germany.
