A man was questioned by detectives on Saturday over the unsolved killing of John “Goldfinger” Palmer, the renowned gangster found dead in his Essex mansion in 2015.The 50-year-old, originally from Tyneside but now living in Southern Spain, went voluntarily into a police station and is now being questioned on suspicion of murdering the Mr Palmer, Essex police said.The number of potential suspects for the killing ran into the tens of thousands, police said, due to the number of victims of Mr Palmer’s crimes. Police at the home of notorious British criminal John ‘Goldfinger’ PalmerCredit:PA Mr Palmer was convicted of a timeshare fraud in 2001 which had 16,000 potential victims as well as being investigated by the Spanish authorities in connection with another alleged property fraud scheme. Police said this put the number of potential suspects in the tens of thousands last month, when they admitted they were “not even close” to finding his killer.Mr Palmer, who earned his nickname after being implicated in the infamous Brink’s-Mat gold bullion robbery in 1983, was shot six times in the garden of his secluded home near Brentwood.In a spectacular blunder, police initially failed to notice that he had been murdered and put his death down to natural causes, attributing the wounds to recent gall bladder surgery. It was not until six days later that Essex police confirmed Mr Palmer had in fact been murdered, probably by a professional assassin using an 8mm.32 calibre pistol fitted with a silencer.”We believe it was very much a contract style killing. The search is not just for the gunman, but the person who wanted Mr Palmer dead,” Detective Chief Inspector Stephen Jennings told an inquest in December.He added: “We are not even close in terms of finishing this inquiry.”Because of Mr Palmer’s lifestyle and previous involvement in criminality, this has been a wide ranging and extensive investigation. A lot of it is based on his lifestyle. “The Brink’s-Mat robbery in 1983 has been one of the potential lines of inquiry. He was arrested on suspicion of smelting gold, he was never convicted of that.”In 2001 he was convicted of a timeshare fraud which had 16,000 potential victims and losses in excess of £33 million. He was sentenced to eight years in prison, so that is 16,000 potential motives.”Mr Jennings said police were also investigating possible links with the Hatton Garden heist, Britain’s biggest ever burglary, of which at least £10 million in cash, jewellery and other valuables, has never been recovered. He told the inquest: “We know he (Palmer) was associated with some of the individuals convicted of that crime.”The hearing was told that Palmer had been moving around his extensive grounds on a green six-wheel garden buggy – seen clearly on CCTV security cameras at the house – and had been making use of a garden burner in one secluded part of the property when his assassin struck.Police believe the gunman lay in wait behind a six-foot wooden fence and monitored Mr Palmer’s movements through a secret spy hole that had been drilled in the fence and the murder was the work of a professional assassin. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.