Authorities said that the elderly suspect, surnamed Lee, had moved out of the 21-storey public rental building in November after prolonged conflicts with his upstairs neighbours.
In the nearly two years that Lee lived in unit 301, he frequently argued with the people living directly above him in unit 401 over noise issues, according to The Korea Times newspaper.
Police had been called to the building in September after a physical altercation, but no criminal charges were filed. Even after moving out, Lee reportedly continued to visit the complex and argue with his former neighbours.
“He was someone the police should have dealt with, not us,” one resident told The Korea Times.
Lee allegedly returned to set the building on fire on Monday morning, about five months after he had moved out. Witnesses reported a loud explosion and flames coming out of units 401 and 404.
