Saad al-Hilli, 50, his wife, Ikbal, 47, and her mother were shot dead along with a French cyclist on a forest road near Annecy in eastern France almost two years ago.
The Surrey couple’s two young daughters survived the attack which has so far gone unsolved.
As police continue to search for a motive, it emerged that Ikbal al-Hilli was briefly married to an American dentist in 1999 without the knowledge of her family.
Prosecutors confirmed reports that the man, identified only as James T, died of a heart attack in Natchez, Mississippi, on September 5, 2012 — the same day of the killings. Members of his family have cast doubt on the cause of death, with one relative even suggesting he may have been killed with a poison dart.
But detectives are not connecting the deaths.
Annecy prosecutor Eric Maillaud said: “He died from a heart attack on September 5, 2012. This was confirmed by an American doctor. No link is being made with the Chevaline killings.”
But Maillaud conceded it opened several interesting lines of inquiry and fresh theories.
He said: “Factually it is very strange that they both died on the same day.
“The percentage of chance is very slim, but as things stand nothing allows us to think that Iqbal was the main target or that her ex-husband was also one.”
“One could imagine anything, including that the ex-husband had her killed because he was disappointed that she had left him and then he committed suicide with a drug that gave him a heart attack without leaving any trace because he couldn’t stand having ordered the murder so he decided to die at the same time as her. Why not? But we have no evidence to back this up.”
“But this was 11 years after they broke up. That’s a long time.”
It also emerged that police last month questioned a 35-year-old Iraqi man following a tip-off from a former jail mate.
The man, Mr S, was traced following claims he once told a fellow prisoner he had been offered “a large sum of money” to kill Iraqis living in the UK.
He was released without charge after it was established he was not in France on the day of the killings and there was no evidence linking him to the al-Hilli family.
Mr Maillaud said: “Investigators were not able to establish that the offer was made and there was nothing to confirm that the Iraqis living in the UK were the al-Hillis. Furthermore, he was not in France on September 5, 2012.”
The bodies of Iraqi-born Mr al-Hilli and his dentist wife were discovered along with that of Mrs al-Hilli’s mother in their BMW on a remote forest route by cyclist Brett Martin.
Passing cyclist Sylvain Mollier, 45, was also found shot dead.
Mr al-Hilli’s brother, Zaid, was arrested on suspicion of murder in June last year but was told in January that he would face no further action after police found there was insufficient evidence to charge him with a crime.
A 48-year-old man was arrested in February but was released from custody after investigators found no direct link between him and the killings.