BEIT SHEMESH, Israel (VINnews) — A 5-year-old boy was killed and his 9-year-old cousin was critically wounded Monday after the two were stabbed during a birthday celebration at a home in Beit Shemesh, Israeli authorities said.

The children were taken to Hadassah Ein Kerem Hospital in Jerusalem. The 9-year-old was unconscious and in critical condition, while the 5-year-old was initially listed in serious condition. His death was later confirmed at the hospital.

A 15-year-old relative who had been watching the children reportedly witnessed the attack. The father of one of the children returned home shortly afterward and found them injured near a swimming pool.

Police arrested a neighbor on suspicion of carrying out the stabbing. Investigators are examining whether the suspect may have been suffering from a mental health crisis or whether a dispute between the families played a role.

Magen David Adom medics described the scene as “shocking,” saying they performed lifesaving treatment and CPR on the 9-year-old before taking both children to the hospital.