Fire officials are examining the site of explosion and fire at an apartment complex in Gyeongsan, North Gyeongsang Province, Thursday. (Yonhap) Police investigating last week's fatal apartment complex fire said Sunday they are considering the possibility that it was an act of vengeance by the suspect against a resident who filed a criminal complaint against him.Police officials are reportedly reviewing several possibilities in Thursday's fire and explosion at an apartment in Gyeongsan, Gyeongsang Province, including a suspicion that it was a targeted attack against a specific individual. The incident led to seven injuries and one death.On the day before the incident, a resident representative of the complex filed a criminal complaint against the 71-year-old suspect surnamed Ryu for making a scene at the management office. Although police had yet to notify Ryu at the time of the deadly attack, residents' testimonies show that he was aware of the charges filed against him.One resident said Ryu was watching as residents filed a police report against him, while another heard Ryu say, "I'll file a complaint, too."Ryu is accused of starting a fire in the management office of the complex around 8:29 a.m. Thursday. He also sustained severe burns in the attack, but went home to get a knife and roamed around the complex shouting, "I'll kill you all."Police launched an official investigation against Ryu, but have not yet interviewed him as he is still being treated for injuries.The suspect is currently being accused of causing death by setting fire to a residential building, punishable by at least seven years in prison and up to the death penalty. But if he is found to have acted out of revenge, he would face harsher punishment for retaliatory crimes, stipulated in the Act on the Aggravated Punishment of Specific Crimes.