Warsaw police are questioning witnesses and reviewing street surveillance videos after a man set himself on fire in the city's center.
Police spokesman Robert Koniuszy said Friday the 54-year-old man was in serious condition at a hospital. He says the man was from outside Warsaw.
Koniuszy says police are gathering evidence to determine his motives.
Polish news portal Wyborcza.pl reports that the man distributed leaflets protesting policies of the country's conservative government before he set himself on fire Thursday.
The portal says he listed the government's hostility to migrants and efforts to control the judicial system. It also says the man had a letter saying the ruling Law and Justice party would be responsible for his death.
RMF FM radio in Poland says he had been treated for depression.