On the morning of his "extremely violent" attack, Harpon bought two knives -- a 33-centimetre long kitchen Online Cigarettes Store USA knife and an oyster knife -- which he kept hidden, Ricard said.
He showed "absolutely no signs of nervousness" as he circled back to police headquarters, according to CCTV footage examined by police, the prosecutor said.
The attack, from his return to the office, the killings and his death by police bullets, lasted seven minutes Newport Pleasure, Ricard said.
He first killed a 50-year old police major and a 38-year old guard who worked in the same office as Harpon and were having lunch at their desks.
He then went to another office on the same floor where he killed a 37-year old administrative worker.
Having failed to enter another office, which was locked, he went down into the courtyard where he stabbed a 39-year old policewoman who later died of her wounds.
He then injured two other people, before the trainee policeman killed him with two shots.
Shortly before the attack he had exchanged 33 text messages with his wife.
The messages exclusively concerned religion, and the attacker ended the conversation with "Allahu Akbar" Cheap Newport 100s cigarettes("God is greatest") and told her to "follow our beloved prophet Mohammed and meditate on the Koran", according to the prosecutor.