Sylvain Mollier was thought to have been shot simply because he stumbled on last month's attack on the British-Iraqi family.
But the ballistics report revealed that he was the first person shot, before the killer turned on the al-Hilli family the website of Le Parisien reported.
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Saad al-Hilli, 50, his wife Iqbal, 47, and her mother Suhaila al-Allaf, 74, were all shot and killed.
Seven-year-old Zainab al-Hilli nearly died after being shot in the shoulder and hit repeatedly around the head by the attacker. She has been unable to help the enquiry in any meaningful way.
Her four-year-old sister survived by sheltering under her mother's skirt in the back of the family's BMW estate car.
Investigators think only one person was involved in the shootings.
Having examined the soles of his shoes, they think Saad Hilli was first shot outside the car and then finished off after he got back in the car and tried to drive off, Le Parisien reported.
After having shot the three members of the family in the car, the killer then turned back to the cyclist and finished him off, investigators think, basing their theory on the different angles of some of entry wounds.
Their reconstruction suggested that the killer had moved around a lot in an apparently disorganised manner, going from one victim to another and then back again.
That seemed to undermine the theory that a professional killer had been behind the killings, investigators told the paper.
