Police investigating a rampage that killed four people in Nagano Prefecture, central Japan, say the suspect likely stabbed one of two police officers he is alleged to have killed after shooting him.

Investigative sources said footage in a drive recorder in the officers' patrol car shows that the suspect stabbed the police officer after firing shots. Two elderly women were also killed in the incident last Thursday.

The victims have been identified as Murakami Yukie and Takeuchi Yasuko, neighbors of the suspect, and Tamai Yoshiki and Ikeuchi Takuo, who belonged to the Nakano Police Station in Nagano Prefecture.

Police have arrested 31-year-old Aoki Masanori for killing Ikeuchi. They are continuing to investigate the deaths of the other three victims, who they also think Aoki killed.

They say the drive recorder footage shows him firing two shots from a hunting rifle into the car window on the driver's side, where Ikeuchi was sitting.

Police sources say Aoki then went to the side of the front passenger's seat and stabbed Tamai, who was trying to open the door and get out. They say the officer died from stab wounds.

Aoki told investigators he killed the two officers, thinking they might shoot him dead. The officers had rushed to the scene in response to an emergency call.