A 47-year-old grandmother was sentenced Tuesday to 16 months in prison for participating in physical abuse that lead to the death of her grandson in February.

The Chiba District Court found Kazue Seki guilty of binding her 3-year-old grandson, Kakeru Yamamoto, to a pillar with a leather belt for 31/2 hours at their residence in the city of Sodegaura, Chiba Prefecture, on the morning of Feb. 13. A public nurse discovered the boy strapped to the pillar.

The boy's 78-year-old great-grandfather, Eisaku, his 49-year-old grandfather, Sakuzo, and his 25-year-old stepmother, Chiemi Yamamoto, also stand accused for their roles in connection with the boy's death.

Prosecutors demanded a two-year prison term for Kazue, saying severe punishment is needed to prevent similar cases of abuse from happening again.

According to the investigation, the boy was confirmed dead at a local hospital Feb. 20, apparently after another round of family abuse.

The boy's corpse exhibited signs of physical abuse and showed he was suffering malnutrition when he died, prosecutors said.

Prosecutors demanded a 21/2-year prison term for the child's great grandfather and are expected to demand prison terms Thursday for the remaining two relatives.