Either there were MOSSAD handlers who had him attack on July 22nd or he was such a big Zionist, he chose that day himself.
King David Hotel bombing
The hotel after the bombing
Jerusalem, Mandate Palestine July 22, 1946
King David Hotel Bomb 91 (Dead) 46 (Injured) Irgun
The King David Hotel bombing was an attack carried out by the militant right-wing Zionist underground organization Irgun on the King David Hotel in Jerusalem on 22 July 1946. 91 people of various nationalities were killed and 46 were injured.
The hotel was the site of the central offices of the British Mandatory authorities of Palestine, principally the Secretariat of the Government of Palestine and the Headquarters of the British Forces in Palestine and Transjordan. The attack, which initially had the approval of the Haganah (the principal Jewish paramilitary group in Palestine) and was conceived of as a response to Operation Agatha (in which widespread raids, including one on the Jewish Agency, had been carried out), was the deadliest directed at the British during the Mandate era (1920–1948). More people were killed than by any bombing carried out in the subsequent Arab-Israeli conflict.
Irgunists planted a bomb in the basement of the main building of the hotel, under the wing which housed the Mandate Secretariat and a few offices of the British military headquarters.
On 22 July 2011, Breivik went to Utøya island, the site of a Labour Party youth camp, posing as a police officer and then opened fire on the adolescents present, reportedly killing at least 68.
He has also been linked with the bomb blasts which had taken place approximately two hours earlier in Oslo, killing at least 8. He was arrested on Utøya and is currently in police custody. Following his apprehension, Breivik was characterised by officials as being a right-wing extremist. The acting police chief, Sveinung Sponheim, said the suspect’s Internet postings "suggest that he has some political traits directed toward the right, and anti-Muslim views, but if that was a motivation for the actual act remains to be seen."
Six hours before the attacks, Breivik posted a YouTube video urging conservatives to "embrace martyrdom" and showing himself wearing a compression garment and pointing an assault rifle.