Video was posted on Instagram on May 19
TokyoReporter
A real estate executive was stabbed in the abdomen and back with a knife
Gender and approximate age are unknown, police said
Police used security camera footage to link the suspects to the theft
Boy surrendered to police on Saturday morning
Girl said, 'I couldn't tell my parents'
Twelve persons were hospitalized after the incident
One of the bodies had already turned skeletal, police said
Suspect was in custody for possessing methamphetamine
