The police in the Commonwealth of the Northern Marianas say they have no indication what sparked the territory's worse mass killing yesterday.
Three people were stabbed to death in the village of San Antonio on Saipan, while a man police suspect was the killer was shot by the first officer on the scene.
That policeman needed medical attention for stab wounds to his elbow and the side of his body after he had been enticed inside a building by the suspected killer.
The four dead were all Asian but police have not yet established which Asian country they came from and whether they were workers or visitors to the territory.
The police commander investigating, Major Edward Manalili, says the killings have stunned the people of Saipan.
"Everyone is pretty much in shock something like this. The victims all suffered multiple stab wounds so it was pretty gruesome."