JERUSALEM (JTA) — The parents of a 4-year-old boy killed in a mortar attack at his home on a kibbutz near the Gaza border in a letter called on the head of the United Nations to speak out about Hamas’ war crimes.

“Daniel was killed from a mortar shell that was fired by Hamas members from an elementary school for boys in Gaza City,” Gila and Doron Tragerman wrote in a letter to U.N. Secretary-General Ban Ki-moon sent on Thursday, the Israeli daily Yediot Acharonot reported. “It wasn’t a stray shell. It wasn’t accidental death.”

The Tragerman family reportedly had left their home during the first three weeks of Israel’s operation in Gaza, but returned nearly a week before Daniel’s death after security officials told residents it would be safe. But rockets began hitting the area again when the cease-fire was broken on Aug. 19.

The family reportedly had planned to leave the kibbutz on the day Daniel was killed by shrapnel from the mortar attack.

The Tragerman’s letter criticized the U.N. commission of inquiry, set up and charged with investigating whether Israel’s actions in the Gaza Strip constitute as war crimes.

“The investigation Committee is not asked to investigate how terrorists shoot out of UN buildings and schools,” they wrote. “The Committee is not asked to investigate how inside buildings of the United Nations and in hospitals in Gaza terrorist infrastructure flourishes and maintains over time, or how from these places terrorist left for activity aimed against innocent people.”

The letter told Ban about their family and their son, what life under the threat of rockets from Gaza has been like for the last several years, and about the day Daniel died.

“He died in our hands, in front of his little sister and best friend Yuval, 3.5 years old. He died in front of Uri, only four months old and right before our eyes, his mother and father. We failed. We couldn’t protect our beautiful and talented baby,” the letter said.