It is unclear if Eric Maillaud's belief is based on crime scene analysis or if Surrey police have found anything significant in Al Saad family home.
The first witness at the murder scene after three members of the al-Hilli family were killed in the French Alps has told the BBC he faced a "dilemma" at whether to leave a girl who had been injured in the attack.
Brett Martin said:
Dragging her on my shoulder may have killed her. I decided to leave her in the recovery position. I was not comfortable in making that decision.
Brett Martin, the first witness on the scene at the al-Hilli family shootings in the French Alps has told the BBC that his opinion "slowly changed" from whether it was a car accident or a shooting.
Mr Martin said he saw the car running and moved the cyclist out of the way of the car. He said he realised that the injuries "did not match the body". He said:
[Zainab al-Hilli] looked from a distance, like she was falling about. But as I approached her I saw she was injured, and there was a lot of blood on her. What it seemed like at the time was a massive car accident.
She was lying semi-conscious. I needed to move her, so I soon gently moved her, clear off the road, and put her in the recovery position. I then moved on. She was very severely injured. It seemed obvious that she had bad head injuries.
It looked just like a Hollywood scene. But unfortunately it was real life.
Assistant Chief Constable Rob Price from Surrey Police told the press today that the investigation into the murder of three members of the al-Hilli family will be lead by French police.
Mr Price said that there would be "inevitable complexities and challenges" of different languages and legal systems, but said that this had been "overcome".
French prosecutor Eric Maillaud, in charge of the investigation into the al-Hilli family shootings told the press that "there were no problems" between UK and French jurisdictions during his visit to the UK today.
Mr Maillaud said the visit would help "reinforce cooperation and understanding" and would help to find a resolution to the investigation.
French prosecutor rules out robbery or carjacking as cause for the Alps massacre, saying its origins "without doubt" in the UK.
Eric Maillaud says Annecy was merely the setting for the murder of Saad Al Hilli, his wife, mother-in-law and a passing French cyclist
France's state prosecutor Eric Maillaud spoke ahead of his visit to the UK today, to assist in the al-Hilli family shootings investigation in which three people were shot dead in the French Alps.
Mr Maillaud said there were three possible theories to explain the killings, as investigators wait to speak to the seven-year-old girl who survived the accident. Mr Maillaud told a press conference in the French city Annecy:
– Eric Maillaud, French prosecutor
Today there are no suspects, but different theories, and I can tell you that in this very complex investigation, there are three possible theories.
There's the theory of a family conflict between the two brothers regarding a sum of money or inheritance. We have some elements concerning the financial conflict between the two brothers, but the brother in Britain denies this, he says he was on good terms with his brother.
We have the theory about the profession of Mr al-Halili and we have the theory about his origins in Iraq.
A French prosecutor and judge are due to arrive in the UK in order to liaise with police teams in the UK in the investigation into the al-Hilli family shootings, Surrey Police have said in a statement. Surrey police said:
The purpose of the visit is to build upon the already good liaison and established cooperation between the French Gendarmerie and Surrey Police teams, given the complex nature of the investigation crossing two jurisdictions.
Surrey Police is continuing to provide all possible support, including the provision of specialist search teams to carry out thorough checks at an address in Claygate, and a Family Liaison Officer (FLO) to assist members of the family involved both in France and the UK.
The seven-year-old girl, whose family was shot dead by a gunman in the French Alps could have been left blinded, according to The Telegraph.
Zainab al-Hilli survived the attack despite being shot in the shoulder and pistol-whipped around the head, bu there are concerns her health is deteriorating.
The facial injuries were reportedly so horrific that she could lose her sight in one eye. A police source was quoted as saying of Zainab:
She suffered multiple facial injuries that caused two subdural hematomas and a fractured orbital bone. She was beaten around the face with great force, the trauma was immense.