A man has been detained in connection with the unsolved case of three British family members and a French cyclist who were shot dead in the French Alps in 2012. Saad al-Hilli, an Iraqi-born engineer, his wife, Ikbal, and her mother, Suhaila al-Allaf, were gunned down in a layby on remote forest road outside the village of Chevaline, near Lake Annecy. The couple’s two young daughters survived the attack. A local cyclist, Sylvain Mollier, was also shot dead at point-blank range after apparently stumbling on the scene. No one has been charged over the attack, one of France’s most notorious recent unsolved crimes. Police sources told French media an unidentified man had been taken into custody and his home searched. The man’s movements and whereabouts on the day of the killings, as well as the days before and after, were being verified, the sources said. Line Bonnet, the public prosecutor in Annecy, said in a statement a person had been arrested at 8am on Wednesday by detectives in Chambéry, adding that further details would be released “after the detention” but that the investigation was covered by judicial secrecy laws. BFM television said the suspect was a married man who had previously been questioned as a witness. The arrest follows a detailed recreation of events by gendarmes in September, on the ninth anniversary of the killings. French and British police have so far failed to make any real progress in the case despite a massive effort involving officers on both sides of the Channel. The bodies of Hilli, 50, and his dentist wife, 47, who lived in Claygate, Surrey, and were on holiday in the region, were found along with that of Allaf in their UK-registered BMW car. More than two dozen used bullet casings were found near the vehicle. In one of many unexplained twists in the case, it emerged that Ikbal’s previous husband, an American dentist, died from a heart attack on the same day as the shootings, although police have said the deaths were not connected. Hilli’s then seven-year-old daughter, Zainab, was pistol-whipped and badly beaten during the attack, possibly after the killer ran out of ammunition, police have suggested. Her sister Zeena, then four, hid in the footwell of the vehicle. Several suspects have previously been detained in connection with the case, including Hilli’s brother Zaid, who was arrested on suspicion of murder in 2013 but later told there was insufficient evidence to charge him with a crime. Zaid, from Chessington, Surrey, admitted he had fought with his brother in October 2011 after months of arguments over a £1m property that the family owned in Claygate, but strongly denied any suggestions he was involved in the killings. A 35-year-old Iraqi man identified only as S was also questioned by police following a tipoff from a fellow former prisoner that he had claimed to have 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. A former soldier in the French Foreign Legion, Patrice Menegaldo, who was living locally at the time and later killed himself in 2015, was named as a prime suspect in a book published three years after the shootings. Detectives suggested he fitted the profile of the professional hitman believed to be behind the crime. The book also contained a claim from Hilli’s brother that there had been a “cover-up” and that Mollier was the killer’s real target. A passing motorcyclist from Lyon was also traced and ruled out of the inquiry.