A jealous husband shot dead his wife and his mother-in-law before turning the gun on himself, at their home in Khon Kaen on Wednesday.
The sound of gunshots at the house in tambon Ban Khok was reported to local police about 3am.
Rescue workers found the bodies of three people, all dead with gunshot wounds, inside the house. They were identified by police as Manee, 52, her daughter Chanadda, 35, and Kraiphop, 39. Their family names were not given.
Police said that Kraiphop believed his wife was having an affair with another man. He had earlier posted the accusation on his Facebook account. Heated arguments followed.
Kraiphop then bought a gun and used it to threaten his wife on Wednesday morning. His mother-in-law was present. When she moved in between them to protect her daughter, Kraiphop shot her. Manee fell to the floor and Kraiphop shot his wife dead and then himself, according to police.
The police did not mention any witnesses to the shooting or explain how they knew what happened.