06/09/2013 10:09 BST | Updated 06/09/2013 10:14 BST

French Alps Shootings: Police Probing Saad Al-Hilli's Recorded Phone Calls

Investigators have gleaned vital clues from recordings of phone calls made by one of the four victims of a brutal gun murder in France.

British engineer Saad al-Hilli, from Claygate in Surrey, recorded all of his telephone calls and the audio files are in the process of being analysed.

Saad al-Hilli was mudered along with his wife and her mother

Mr al-Hilli and his wife Ikbal were gunned down on 5 September last year as they holidayed near Annecy, in south east France.

Mrs al-Hilli's mother Suhaila al-Allaf and local man Sylvain Mollier also died, and the al-Hillis' daughter Zainab was shot in the shoulder and beaten, but survived.

Today Annecy prosecutor Eric Maillaud said: "The victim recorded all his telephone conversations. We therefore have some very precise details."

Mr al-Hilli's brother Zaid, who is from Chessington, Surrey, is due to answer police bail next month after he was arrested on suspicion of conspiracy to murder amid claims he doctored documents to ensure he inherited the family estate.

Mr Maillaud said the inheritance dispute remains a central line of inquiry, and they are looking into the brothers' father's property in Baghdad.

French and British investigators held a joint press conference in Annecy on Friday to give an update on the investigation, just over a year since the family was killed.

Although no charges have been brought in the case, Mr Maillaud said: "We have made great advances."

The horrific murder scene was discovered by cyclist Brett Martin who found Mr Al-Hilli, 50, his 47-year-old dentist wife and her elderly mother blasted to death in their BMW.

Zainab was ''stumbling'' around, bleeding and ''moaning'' near the car, and her four-year-old sister Zeena lay hidden under her mother's corpse and was only discovered eight hours after the murders.

The two children returned to the UK soon after the killings.

Zaid al-Hilli denied any knowledge of why his brother was killed when approached by Sky News.

When asked if he knew why his brother died, he told the broadcaster: ''No, no idea, absolutely none.''