Russian journalist Arkady Babchenko has died after being shot at his home in Kiev, according to police.
Mr Babchenko, 41, was reportedly found bleeding in their apartment block by his wife and died in an ambulance.
After writing about a crashed Russian military plane in 2016, Mr Babchenko said he received death threats and left his home country.
He previously worked as a presenter on Ukrainian channel ATR TV, and has written about his military service.
Ukrainian law enforcement confirmed his death in a Facebook post, written in Ukrainian.
Kiev police chief Andriy Kryshchenko also told the media they suspected Mr Babchenko was killed due to his “professional activities”.
Mr Babchenko has criticised the Kremlin in recent years, standing in opposition-led elections against the government in 2012 and denouncing Russia’s actions in Syria and eastern Ukraine.
In December 2016, Mr Babchenko wrote a Facebook post about a crashed Tu-154 transport plane, which fell into the Black Sea while carrying a Red Army choir to Syria.
He claims this Facebook post, in which he described Russia as an “aggressor”, led to death threats and abuse from the Russian state, writing in a piece for The Guardian that this forced him to leave “a country I no longer feel safe in”.
While studying law in Moscow aged 18, Mr Babchenko was conscripted into the Russian army and served in the Chechen wars in the 1990s.
His memoir, One Soldier’s War, chronicles his experiences in the conflict, which claimed the lives of tens of thousands on both sides.
He then became a journalist, working for a number of different outlets.
Mr Babchenko even wrote for the BBC, reporting from the scene of a Ukrainian army helicopter shot down in the east of the country in 2014.