Police will investigate to see if negligence was a factor in the heart attack death of a 13-year-old boy Wednesday after a full day of judo practice at a training camp in Awaji, Hyogo Prefecture.

Yuki Nagahara complained of feeling sick during the practice Tuesday, but the 29-year-old camp instructor, who later slapped the youth and kicked him in the stomach, did not take him to a hospital, according to the the Kobe board of education. He collapsed later that evening and was taken to a hospital, where he died early Wednesday.

Police believe Yuki Nagahara might still be alive if he had been hospitalized earlier and will question the instructor and others at the camp again to see if he is responsible.

According to the board of education, which looked into the death, Nagahara told the instructor during training that he had a headache and felt he might be suffering from the flu, but the instructor did not do anything.