Liel Ifergan, 26, has been named as the main suspect in the murder of seven-year-old Hillel Mordechai Dadon in Beit Shemesh.
Ifergan allegedly stabbed Dadon and his four-year-old cousin, who was seriously wounded, while the two boys were playing in a pool.
Ifergan lives near the scene, and police arrested him shortly after the murder.
According to suspicions, Ifergan arrived near the apartment a few hours before the deadly incident, briefly spoke with the homeowner, left the area, and later returned and stabbed the children with a sharp object.
His detention has been extended until next Tuesday.
Chief Inspector Guy Avrahami, deputy head of interrogations at the Jerusalem District Central Unit, addressed developments in the investigation, saying, "We arrived at a very difficult scene, where a young child lost his life while playing in a pool."
"At this stage, we are focusing our investigative efforts on understanding exactly what the suspect's motive was and what led him to harm the children. The work of gathering evidence and putting together the pieces of the puzzle continues, with the aim of uncovering the truth and bringing the suspect to justice to the fullest extent of the law," he added.