The 18-year-old male candidate allegedly opened fire at three GSDF personnel at the organization's Hino shooting range during live-fire training in Gifu City, central Japan, on Wednesday.
The suspect told police he shot a GSDF member who was next to him because he stood between himself and the 52-year-old instructor and blocked his way.
The shooting left the instructor and a 25-year-old man dead, and another 25-year-old man hospitalized.
Police arrested the candidate on suspicion of attempted murder on Wednesday. He was sent to prosecutors on suspicion of murder on Thursday morning.
Bullet-proof vests not worn at training
The GSDF said that about 120 people were taking part in the training when the incident occurred.
They said about 70 SDF candidates and around 50 SDF members, including instructors, were at the facility.
Participants were all wearing steel safety helmets, but did not wear bullet-proof vests. The GSDF officials said the training was conducted according to its rules.
They said the gun used in the shooting was a Type-89 5.56 mm assault rifle. The weapon is standard issue, used by the GSDF across the country.
Officials conducting on-site investigation
The GSDF and police are conducting an on-site investigation. Their vehicles have been entering the shooting site since Thursday morning.
Mourners also gathered in front of the site to pay their respects.
A 19-year-old man from Gifu City said that he believes the deceased victims worked hard to protect people's lives. He said that he wants the GSDF to take measures to prevent such incidents from happening again.
Sources: Suspect loaded rifle before he was supposed to
Sources at the defense ministry said they believe that the suspect had loaded his gun before the training called for doing so.
Participants in GSDF live-fire training are supposed to receive live rounds after they enter the firing range and put the bullets into their magazines as instructed. They are not supposed to load their rifles until they are standing in position to shoot.
Other sources said the candidate fired four times while he was waiting for his turn to shoot. They said he fired the shots one by one, rather than in rapid succession.
GSDF releases victims' names
The GSDF has released the names of those killed and injured in the shooting, who served in its 35th Infantry Regiment.
It identified the dead victims as 52-year-old Sergeant 1st Class Kikumatsu Yasuchika and 25-year-old Sergeant 3rd Class Yashiro Kosuke.
It also said 25-year-old Sergeant 3rd Class Hara Yusuke was injured.
GSDF Chief: Victims weren't training suspect
GSDF Chief of Staff General Morishita Yasunori said that the victims worked at the shooting range and were not in roles in which they directly taught trainees.
"Further investigation will determine what kind of contact they had [with the suspect]," Morishita said at a news conference on Thursday afternoon.
He also said that he had instructed the force to resume shooting training as soon as its safety can be assured.
The GSDF has suspended all training involving guns following Wednesday's incident.