TULSA, Oklahoma - A woman is dead after Tulsa police say a man shot her then took his own life. 

Investigators found a letter in another language, a key piece of evidence in the case. 

It all started when a man called police to report his wife missing. Officers said they found out she was having an affair with another man, who ended up killing her. 

Tulsa police found a man and woman dead inside a bedroom of a house near 41st and 129th East Avenue.

Officers said the woman was having an affair with the suspect and things took a dangerous turn at his house Saturday night. 

"A friend of the suspect noticed on his Facebook page that he had a woman tied up and was beating her," said Tulsa Police Sergeant Dave Walker. 

"You wonder what could have happened. What could have caused someone to get into that type of situation to where they would resort to something like that," said neighbor Boyd Utley. 

Investigators said while a motive isn't clear, they've determined she probably wasn't going to leave her husband for him. 

When police got to the suspect's home, they heard a muffled sound coming from inside. 

"Officers heard some sort of noise like gunshots, not very discernible, but it was a popping noise from inside and that happened three times," Walker said. 

The man left behind some letters, written in Hmong.

Walker said the translation by two officers who know the language is invaluable to the investigation. 

"There is writings in there about suicide, what to do, some money that was in there. And it was written on there to use that for the funeral," said Walker. 

Boyd Utley was surprised to learn what happened down the street in his quiet neighborhood he considers safe.  

"I've lived here since 1999," Utley said. "We have occasional break-ins here, like any neighborhood."

The man and woman's names have not been released. 

This marks Tulsa's 11th homicide of the year.