In the early evening of 4 July 1928, a fabulously wealthy businessman named Alfred Loewenstein boarded his private plane at Croydon Airport. It was a routine flight that would take him across the English and French coastlines before landing at Brussels, where Loewenstein lived with his wife, Madeleine.

Alfred Loewenstein

Loewenstein was instantly recognizable to the staff at the airport. Indeed, he was recognizable wherever he went. He was a spectacularly wealthy entrepreneur: so wealthy that he was widely known as the world’s richest man.

Already rich before the First World War, his fortune had increased dramatically in the peace that followed. His various companies provided electric power for developing countries and before long he was being sought out by presidents and prime ministers around the globe.

But he also had many enemies. In 1926, he established International Holdings and Investments, which raised huge amounts of capital from wealthy investors. By 1928, these investors wanted some return on their money. And they wanted it sooner rather than later.

Loewenstein was pleased to be flying home on that July day in 1928. It was a fine evening for flying with scarcely a cloud in the sky. The pilot, Donald Drew, assured him that it would be a smooth flight.

There were a total of six people on the plane, in addition to Alfred Loewenstein. Pilot Drew stood by the doorway of the aircraft as the passengers and crew boarded. The other people in the cabin included Fred Baxter, Loewenstein’s loyal valet, and Arthur Hodgson, his male secretary. There were also two women, Eileen Clarke and Paula Bidalon, his stenographers.

In the cockpit were Drew and Robert Little, the aircraft mechanic. The cockpit was a sealed unit with only a porthole connecting it to the rest of the plane. Once the Fokker had taken off, Drew and Little had no direct access to the cabin.

Shortly after 6 p.m., the Fokker FVII, a small monoplane, set off down the grass runway. Within minutes the plane was airborne and climbing to its cruising altitude of 4,000 feet. Before long, everyone on board could see the Kent coastline below. A minute or so later, they were flying over the English Channel.

At the rear of the Fokker’s cabin there was a windowless door that led into a small toilet. This room also had an exterior door. This door was clearly marked EXIT and was equipped with a spring-loaded latch controlled from inside. It took two strong men to open it in mid-air, due to the slipstream pressing against it.

Loewenstein spent the first half of the flight making notes. Then, as the plane headed out over the Channel, he went to the toilet compartment at the rear.

According to statements later made by Baxter ten minutes passed and he had still not returned to his seat. Baxter grew concerned and knocked on the toilet door. There was no answer.

Worried that Loewenstein might have been taken ill, he forced open the door. The toilet was empty. Alfred Loewenstein had disappeared into thin air.

An obvious course of action would have been for the plane to divert to the airstrip at St Inglevert, which lay between Calais and Dunkirk. Here, the pilot could have alerted the coastguard to Loewenstein’s disappearance. Instead, Donald Drew landed the plane on what he believed to be a deserted beach near Dunkirk.

In actual fact, the beach was being used for training by a local army unit. When the soldiers saw the Fokker coming in to land, they began running along the beach to meet it. It took them six minutes to arrive at the stationary plane, by which time the passengers and crew had disembarked.

They were initially questioned by Lieutenant Marquailles, but he was unable to make any sense of what had happened. Pilot Drew behaved particularly strangely, evading his questions for half an hour until finally admitting that they had lost Alfred Loewenstein some-where over the English Channel.

Drew was next interrogated by a professional detective named Inspector Bonnot. The inspector confessed to being extremely puzzled by what he was told. ‘A most unusual and mysterious case,’ he said. ‘We have not yet made up our minds to any definite theory, but anything is possible.’

He didn’t arrest anyone and even allowed the plane to continue its flight to St Inglevert and then back to Croydon.

The ensuing investigation was bungled from the outset. Loewenstein’s body was finally retrieved near Boulogne on 19 July, more than two weeks after his disappearance. It was taken to Calais by fishing boat where his identity was confirmed by means of his wristwatch.

A post-mortem revealed he had a partial fracture of his skull and several broken bones. Forensic scientists concluded that he had been alive when he hit the water.

A diagram of the plane.

The mystery of how he fell to his death remained unanswered, though there are many theories. Some said the absent-minded Loewenstein had accidentally opened the wrong door and fallen to his death. This was most unlikely, given that it was virtually impossible to open the door in mid-flight.

Others said he’d committed suicide, perhaps because his corrupt business practices were about to be exposed.

A far more plausible and sinister explanation is that Loewenstein was forcibly thrown out of the plane by the valet and the male secretary, possibly at the behest of Loewenstein’s wife, Madeleine. She had a very frosty relationship with her husband and was desperate to get her hands on his fortune.

One thing is clear: all six people on board were almost certainly privy to the murder. Indeed, they had probably planned it carefully in advance.

One theory as to why the Fokker landed on the beach was so that a new rear door – already stowed on board the plane – could be fitted to replace the one jettisoned over the Channel. This fits neatly with the story of a French fisherman who recalled seeing something like a parachute falling from the sky at precisely the moment Loewenstein went missing. This ‘parachute’ was quite possibly the rear door.

If the door and Loewenstein were jettisoned over the Channel, it was the perfect crime. No one was ever charged with the murder, nor even directly accused. As for Loewenstein, he was so unpopular that he ended up being laid to rest in an unmarked grave.

Even his ‘grieving’ widow, Madeleine, didn’t show up. She doubtless had more important matters to attend to, organising and investing the fortune that she had just inherited.

This excerpt is from Fascinating Footnotes by Giles Milton, published by John Murray.