Police in central Vietnam said a man, who was saved after trying to kill himself, is the prime suspect in the violent deaths of his wife and her father, local media reported.
Nguyen Hai Liem, 48, is being treated at a hospital in Binh Thuan Province after the suicide attempt on Friday.
Police said he allegedly stabbed his wife, Do Thi Thu Suong, several times at around 1 a.m after he caught her in the bedroom with another man.
Suong, 44, died instantly while the man who was with her managed to run away.
Her father, Do Van Son, who lived next door, heard her scream and came over to check.
Liem stabbed the 63-year-old man several times, who died soon later, police said.
They said Liem then stabbed himself in the chest.
He was rushed to a local hospital in critical condition.
Police said they are watching him closely.