A cyclist who stumbled across the French Alps massacre has described finding "heads with bullet holes in them" in a scene reminiscent of a Hollywood film.
Brett Martin likened the carnage in the secluded car park to a set from TV crime series CSI Miami as the man leading the investigation said the clue to the four murders lay in Britain.
Mr Martin was the first witness to arrive at the spot where engineer Saad al-Hilli, 50, his dentist wife Iqbal, 47, and her elderly mother were blasted to death.
Speaking for the first time today, he told how he found the al-Hillis' daughter Zainab, seven, "stumbling" around, bleeding and "moaning", close to the family car.
Next to the BMW lay the body of Sylvain Mollier, 45, a French cyclist who apparently stumbled across the attack.
The wheels of the vehicle itself were still spinning and its engine was revving. Inside, Mr Martin made out three bodies.
"It was pretty much what you would imagine a set from (TV crime series) CSI Miami would be like," he told the BBC.
"There was a lot of blood and heads with bullet holes in them."
He added: "I've never seen people who have been shot before... it seemed to me just like a Hollywood scene and if someone had said 'cut' and everyone had walked away, that would have been it.
"But unfortunately it was real life.
"It became quite obvious, now, taking stock, that it was a gun crime."
His recollection of events emerged as Annecy's chief prosecutor Eric Maillaud met his British counterparts working on the case at the al-Hilli family home in Claygate, Surrey.
Mr Maillaud - who was accompanied by examining magistrate Michel Mollin, another senior member of the inquiry team - said it was "without any doubt that the reasons and causes (for the killings) have their origins in this country".
Police have revealed they are probing three lines of inquiry, focusing on Mr al-Hilli's work, his family and links to his native Iraq.
The aerospace engineer had been holidaying with his relatives at a campsite near Lake Annecy when they were attacked at 4pm last Wednesday.
Mr Martin, a former RAF pilot, recalled how he set out that afternoon for a bike ride at about 2.30pm.
But as he climbed to the top of a hill in the Combe d'Ire forest, near Chevaline, he was faced with a bloodbath.
"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."
There was no sign of the al-Hillis' younger daughter Zeena, four, who had been cowering underneath her mother's body during the brutal attack.
Mr Martin turned his attention to Zainab, first moving her body from where it lay in front of the car, fearing the vehicle could lurch forward and crush the child.
He placed her in the recovery position and a few minutes later, she fell unconscious.
The little girl appeared "severely injured" and there was "a lot of blood", he said.
Mr Martin moved on to treat Mr Mollier, using basic medical skills gleaned during his RAF training.
"It seemed to me like he was probably dead," he said.
"I could not feel a pulse and the most obvious thing was the totally inanimate body."
The occupants of the BMW were in a similar state.
"The thing that struck me was their complete inanimate nature," he recalled.
Mr Martin, who was forced to break the driver's window to switch off the car's engine, said he wanted to call for help but had no reception on his mobile phone.
The former serviceman, a father himself, realised he would have to leave the scene to make the call but this left him with a dilemma - whether to take Zainab with him, or leave her where she lay.
Fearing he could do more damage - and possibly kill her - by lifting her, he set off on his bike.
"This wasn't a very comfortable decision to have to make," he said.
The cyclist has been credited for potentially saving Zainab's life. The child, who was shot in the shoulder and badly beaten around the head, is now recovering in hospital.
Today a police guard remained outside the al-Hilli family home as officers carried out a fingertip search of the drive, front garden and front hedges.
Later, an officer was seen drilling holes into an overhanging roof in the porch area of the home.