Maxim Borodin was found severely injured by neighbours in Yekaterinburg on Thursday.
He died at a hospital on Sunday.
Local officials said no suicide note was found and the cause of the fall remains unclear.
However a friend revealed that Borodin had said his flat had been surrounded by security the day before.
Vyacheslav Bashkov said Borodin had contacted him at five o’clock in the morning on Wednesday, April 11, saying there was ‘someone with a weapon on his balcony and people in camouflage and masks on the staircase landing’.
In March, Borodin wrote about bodies believed to be those of mercenaries being delivered to a regional village.
Thousands of mercenaries reportedly have been deployed to Syria by a shadowy contracting company believed to be bankrolled by Yevgeny Prigozhin.