The scene of the shooting of a British-Iraqi family in France resembled something from a TV crime series, a British man who was first on the scene said on Thursday.
"It was pretty much what you would imagine a set from (TV crime series) 'CSI Miami' would be like," Brett Martin told the BBC, in his first television interview.
"There was a lot of blood and heads with bullet holes in them."
He said one of the family's daughters, seven-year-old Zainab al-Hilli, was "prone on the road, moaning, sort of semi-conscious" when he stumbled across the scene in a car park in Annecy.
Martin, a former member of Britain's Royal Air Force (RAF), said he came across the scene of devastation after he had set out for a bicycle ride from his base in the French Alps at about 2:30 pm.
As he climbed a hill near Chevaline last Wednesday, he was faced with a bloodbath, starting with a French cyclist who had been shot dead.
"It was the sort of thing you would never in your life expect to come across," he said.
"As I approached the scene, the first thing I saw was a bike on its side. I had seen the cyclist ahead of me much earlier so I thought he was just having a rest.
"As I got a little bit closer, a very young child stumbled out onto the road and at first I thought she was actually just playing with her sibling because she sort of looked, from a distance, as if she was falling over, larking about like a child would.
"However, as I approached her it was obvious that she was quite badly injured and there was a lot of blood on her.
"As I got even closer, I then saw the car with its engine revving and its wheels spinning. It seemed at that moment in time like there had been a terrible car accident."
Investigators say Zainab was shot in the shoulder and beaten.
Her parents, Saad and Iqbal, her grandmother and Frenchman Sylvain Mollier - the passing cyclist - were shot dead.
Zainab's four-year-old sister Zeena was found unhurt eight hours after the attack after hiding under the skirts of the dead women.
Eric Maillaud, the French prosecutor in charge of the investigation into the killings, said on Thursday after arriving in Surrey, the area of southeast England where the family lived, that the cause of the killings lay in Britain.
"We are perfectly aware that Annecy is just the chance location of this drama and that it seems that the origin, the causes and the explanation are here," he told journalists in the town of Woking in Surrey.