An official Russian investigation into the death of Kremlin critic Alexei Navalny was redacted to remove any indications of possible poisoning, The Insider reported, citing “hundreds” of documents it said it had obtained.

Navalny’s widow revealed last month that she received a letter from Russian investigators claiming there were no signs of foul play in her husband’s death at an Arctic penal colony in February. The letter stated that no toxic substances were found in his body, attributing his death to “a range of illnesses”.

However, The Insider published what it claims is the unredacted version of the same letter, which included details that Navalny had “laid on the floor and began complaining of sharp pain in the abdominal area” before experiencing convulsions, vomiting and losing consciousness.

The redacted version received by Yulia Navalnaya only mentioned a “sharp deterioration” in the activist’s health, after which prison doctors placed him in a medical ward and called an ambulance. The Insider did not disclose who may have redacted the documents or at what stage the alterations were made.

“These symptoms can hardly be explained by anything other than poisoning,” said Alexander Polupan, a doctor who treated Navalny after his 2020 poisoning by the Soviet-era nerve agent Novichok. Polupan told The Insider that Navalny may have been exposed to an organophosphorus agent, possibly applied internally.

Also known as nerve agents, organophosphorus agents are highly poisonous chemicals that work by preventing the nervous system from functioning properly.