In a lay-by on a mountainside road in the French Alps, three members of the same British family and a cyclist were gunned down in 2012.
The young daughters of the Surrey couple killed were the only survivors of the shocking murders, which happened almost 10 years ago close to Chevaline, near Lake Annecy, France.
An arrest was made earlier this year, with the prosecutor in Annecy, saying a person had been taken into custody in relation to the investigation. However they later released and eliminated the man from Lyon from their enquiries.
Now a documentary about the case is set to air on TV.
Here’s what you need to know about the case and the latest developments.
What happened in the shootings and who were the victims?
Saad al-Hilli, 50, his wife, Iqbal, 47, and her mother Suhaila al-Allaf, 74, were shot dead on a road near Lake Annecy in eastern France on 5 September, 2012.
Their two young daughters survived the horror attack, but 45-year-old cyclist Sylvain Mollier was also killed.
Zeena, who was four years old at the time, was discovered hiding under her mother’s body inside the car, while Zainab, 7, was injured after being shot and beaten.
The bodies of Iraqi-born engineer Mr al-Hilli and his dentist wife, who lived in Claygate, Surrey, were discovered along with that of Mrs al-Hilli’s mother in their BMW on a remote forest route. The family, from Surrey, had been on a camping trip.
In a bizarre twist, Mrs al-Hilli’s previous husband, an American dentist named only as James T, died from a heart attack on the same day as the couple, but police said there was no link to the murders.
The attack took place in a lay-by on the mountain-side road at about 3.45pm .
Twenty-five shots were fired in total.
Mr Mollier, who was shot seven times, was killed near the BMW.
What has happened with the case since 2012?
Suspects previously arrested in connection with the case include an Iraqi prisoner known as Mr S who was claimed he had been offered “a large sum of money” to kill Iraqis living in the UK.
Mr al-Hilli’s brother, Zaid, was also arrested on suspicion of murder in 2013 but was later told he would face no further action after police found there was insufficient evidence.
In September 2017, after five years of investigation, French police said they had “no working theory” to explain the murders and no suspects.
When is Murder in the Alps on TV?
The three-part documentary series will start on Channel 4 at 9pm on Sunday 26 June.
It will re-examine the case with the use of archive footage and interviews with victims’ friends and family, witnesses, former suspects.
Mr al-Hilli’s brother, Zaid, took part in the series, and told Radio Times: “I needed to tell my side of the story, to show how much this very hurtful episode in our lives affected me and my loved ones,”
He spoke of how he had been at his Surrey home when he heard the news of the shootings on TV - only later in the day did he learn that it was members of his family.
He told the publication of how his own arrest on suspicion of conspiracy to murder had affected him and his anger over it and the “huge relief” he felt when he was told he wasn’t being charged.
The 63-year-old said: “All of a sudden you are at the heart of a storm. You’re trying to understand what happened, then the next minute you are being accused of something you know nothing about.’’
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