(CNN) -- A man in eastern Austria used a homemade firebomb to kill his wife's elderly parents, police said Saturday.
The 48-year-old man then tried to commit suicide by stabbing himself in the stomach, police said. He is in an induced coma but is expected to survive.
The incident happened at 10 p.m. (4 p.m. ET) Friday in Hartberg, a town in Austria's Styria region, about 22 miles (35.5 kilometers) from the Hungarian border, said Chief Anton Kiesl of the state police homicide division.
Kiesl said the man spread gas in the room of his 84-year-old in-laws and then lit a homemade propane gas bottle and threw it at them, burning them alive.
The mother-in-law had diabetes, and her legs had been amputated, so she was unable to flee and died in her bed, Kiesl said. The father-in-law was able to flee but died soon afterward; police found his body on a garden bench near the family's apartment, Kiesl said.
The attack set one room of the apartment on fire, but firefighters were able to keep it from spreading to neighboring apartments, he said.
Kiesl said police don't know the man's motive.
CNN's Ben Brumfield contributed to this report.
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