The uncle of a 6-year-old boy found dead in Kobe instructed other family members to prepare the suitcase used to discard the boy's body, investigators said Monday, citing the boy's grandmother.

The grandmother, 57-year-old Yumiko Hosaka, who was found on the street after allegedly being hit with a steel pipe by her children and confined at their home, says that Daichi Hosaka, 32, gave the instructions to his siblings Saki Hosaka, 34, the boy’s mother, and twins Tomomi Hosaka and Asaka Hosaka, 30, police sources said.

Police arrested the four siblings for allegedly assaulting the grandmother, and are investigating their involvement in the death of the boy.