Alexei Navalny was about to be released in a prisoner exchange when he died, according to his ally Maria Pevchikh.
She said the Russian opposition leader would be exchanged for Vadim Krasikov, a Russian killer serving a life sentence for murder in Germany.
Ms Pevchikh claimed that two US citizens currently detained in Russia would also be part of the deal.
She added that the negotiations reached their final stage on February 15.
The next day, Navalny died in his cell at the prison colony in Siberia, where he had been held for 19 years on charges widely seen as politically motivated. Prison officials said the 47-year-old became unwell after “walking.”
In a video posted on Navalny's YouTube channel, Ms. Pevchikh, who is the head of his anti-corruption Foundation (FBK), said negotiations on a prisoner exchange have been underway for two years.
She added that after Russia's large-scale invasion of Ukraine began in February 2022, “it was clear that Putin would stop at nothing” and that “Navalny must be released from prison at any cost, and urgently.”
According to Ms. Pevchik, Navalny was to be released under a humanitarian exchange, and American and German officials were involved in the talks.
She added that the process finally resulted in a concrete prisoner exchange plan in December.
Vadim Krasikov, a Russian convicted of shooting former Chechen rebel commander Selimkhan Khangoshvili in the head at close range in Germany in 2019, was part of the deal.
Pevchikh said two American citizens currently detained in Russia would also be exchanged, but she did not name them.
According to Ms. Pevchikh, Russian President Vladimir Putin changed his mind at the last minute. She said he “could not tolerate the release of Navalny” – and since there was an agreement “in principle” for Krasikov's release, Putin decided to “just get rid of the bargaining chip.”
“Putin has gone crazy because of Navalny’s hatred,” Pevchikh said. “He knows Navalny could have beaten him.”
A German government spokesman said on Monday that the government “cannot comment on reports” of the planned prisoner exchange at this time.
Within an hour of being posted, Ms Pevchikh's video had hundreds of thousands of views.
The Kremlin has not yet responded to the allegations made by Ms Pevchikh, but President Putin's spokesman Dmitry Peskov previously said allegations of government involvement in Navalny's death were “ridiculous”.