A couple and their three-year-old daughter were killed when a fire broke out in their house Sunday in the southern province of Kien Giang.
The incident happened at nearly 1 a.m., totally destroying the house of Danh Manh, 33, in Hon Dat District.
Police found a can of petrol at the site and the door was locked.
According to Manh's neighbors, they'd heard Minh and his wife, 22-year-old Nguyen Thi Cam Thuy, have an argument the day before.
Some locals told Thanh Nien the couple had frequent arguments because Manh suspected Thuy of having an affair; and that he once claimed he would burn his family and himself to death.
The couple had another daughter, ten years old, who was at her grandmother's home when the fire broke out.