The widow of deceased Russian opposition leader Alexei Navalny is pushing back on a new report from investigators claiming he died as a result of an irregular heartbeat and a combination of diseases, calling the findings a "rather pathetic attempt to hide what happened -- a murder." 

The declaration comes six months after Navalny – a fierce critic of Russian President Vladimir Putin – died at a penal colony in Siberia. Russian officials at the time said Navalny reported feeling unwell following a walk before losing consciousness and dying.   

Investigators are now claiming in a report shared Wednesday by Navalny’s widow Yulia Navalnaya that the 47-year-old passed away after suffering from a variety of ailments, including arrhythmia and cholecystitis, the swelling of a gall bladder.  

"The truth is that this is not a diagnosis, not the results of a test, but a mockery. This is another rather pathetic attempt to hide what happened -- a murder," Navalnaya wrote on Navalny’s official website. "And everyone who writes these papers, writes these false reports -- are accomplices to this murder." 

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Russian opposition activist Alexei Navalny takes part in a march in memory of opposition leader Boris Nemtsov in Moscow, Russia on Feb. 29, 2020. (AP/Pavel Golovkin)

"I showed this diagnosis to my doctors. They all came to the same conclusion: they opened it up, examined it, but couldn't find anything -- no blood clot, no signs of a heart attack or stroke either," she added. "So they wrote about ‘arrhythmia’ to at least write something. Because people don't just die like that." 

"All these chronic diseases, like the gastroduodenitis and pancreatitis listed by the investigator... Well, excuse me, every third person in Russia has such diseases. Suddenly, in an hour, you don't die from such things. But even if we assume that they existed... why weren't they diagnosed in the numerous colonies where Alexei was? Why wasn't he treated? Why was such a sick person sent to a punishment cell and kept there for months?" Navalnaya continued. 

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Russian President Vladimir Putin and Yulia Navalnaya, the wife of Russian opposition leader Alexei Navalny. (Kai Pfaffenbach/Pool Photo via AP)

"There can be one explanation for this. The only one. They killed him, and now they are trying to cover up the tracks as much as possible," she said. 

"If Putin and his obliging comrades... think that we will now shrug our shoulders and say ‘well, okay, so no’ -- they are deeply mistaken. The lawyers will appeal every such document. We will demand that a criminal case be opened," Navalnaya concluded. "I demand that they hand over to us all the medical documents, including the autopsy report... and also that they hand over all of Alexei's personal belongings." 

Russian opposition leader Alexei Navalny appeared in court via video link on Thursday, Feb. 15, a day before his reported death at a penal colony in northern Russia. (Russian Federal Penitentiary Service/SOTAvision/AP)

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In February, President Biden said President Biden said there is "no doubt" that Navalny’s death was a "consequence of something that Putin and his thugs did."