Officer remains in serious condition at a hospital, police said
Suspect told police, 'It is sad to die alone'
Woman suffered several stab wounds to her abdomen and other parts of her body, police said
Locations believed to be linked to a cultivation ring
Security camera footage shows him wearing a knit cap, breathing mask, a green jacket and black pants
Suspect told police, 'I didn't do it'
One suspect said, 'I've been to Japan in the past'
After the incident, the suspect is believed to taken a train for JR Yamagata Station, police said
Suspect allegedly ordered the hit over the telephone, police said
Results of an autopsy revealed that the victim died due to brain damage as a result of a skull fracture, police said