A private plane found with more than $5m (£4m) in cash, fake gold, guns and ammunition on board is at the centre of a deepening investigation in the Zambian capital, Lusaka.

Everyone knows the aircraft flew from the Egyptian capital, Cairo, and landed a fortnight ago in Zambia, but that is where the certainties stop. So far nobody in Egypt or Zambia admits to chartering the plane or owning its contents.

With so many questions unanswered rumours have been swirling.

Could those involved be high-level Egyptian or Zambian political or military figures? Was this a one-off flight or the first out of hundreds to finally be rumbled?

What is known is that all six Egyptians aboard the aircraft and others who joined them at Lusaka's airport are due to appear in court on Monday.

Some of the Zambians who are being held have been charged with espionage and obtaining money on false pretences. The Egyptians have not yet been charged.

The world might have remained oblivious to it all were it not for a journalist whose fact-checking website, Matsda2sh, accused officials in Egypt of involvement in the incident.

Journalist disappears

Soon after that Egyptian plainclothes security forces raided Karim Asaad's Cairo home in the dead of night and arrested him.

At first he just disappeared. Nobody knew where or why Mr Asaad had been taken.

Then independent Egyptian journalists published documents over social media purportedly taken from the Zambian police investigation into the cash-filled aircraft.

These reportedly named three Egyptian military officers and a senior police officer among those arrested, backing up Mr Asaad's allegations.

A barrage of protests on social media, many of them from fellow journalists, led to his release two days later. What exactly he had been arrested for remains another mystery.

The Egyptian authorities would only say that the aircraft mentioned on Mr Asaad's website was privately owned and merely transited through Cairo. In other words, the country and its officials had nothing to do with the case.

Soon after that the spotlight shifted to Zambia after the plane touched down at Lusaka's Kenneth Kaunda Airport.

Somehow, it seems, a Zambian man carrying bags of what looked like gold was allowed to stroll through security and meet the newly arrived Egyptians on the plane.

Nobody appears to know who authorised this but, according to Zambian media reports, a few cash handouts had helped ease his path.

After he climbed aboard the man allegedly sold a portion of the supposed gold he was carrying to the men on the plane. They then asked him for more.

What is not clear is if they managed to discover that what he was selling was actually counterfeit before security staff arrived to search the aircraft.

The arrest, it seems, was not straightforward.

Several of the officers who entered the plane are now being investigated for allegedly receiving up to $200,000 each from the Egyptian nationals aboard the plane. It is claimed this was their reward for allowing the plane to take off without arresting anyone.

When word somehow got out that wads of money on the plane were allegedly changing hands, another group of security staff charged onto the aircraft and arrested those inside.

Gold bar puzzle

Presumably the suspects had trouble explaining what they were doing with millions of dollars in cash, several pistols, 126 rounds of ammunition and what looked like more than 100kg of gold bars.

The gold bars were particularly puzzling.

It turned out that, as well as gold, they were made from a mixture of copper, nickel, tin and zinc. All that glitters is clearly not gold.

It seems the Egyptians aboard the plane may have been saved from a very bad deal.

The Zambian lawyer acting for one of the 10 arrested men said another mystery was why the security forces seemed so bad at maths.

Makebi Zulu told the BBC that at first police said they had found $11m in cash. This, he went on, was later downgraded to around $7m before finally settling on the sum of $5.7m.

One possible explanation could lie in reports that nearly half of the money had been taken off the plane before the arresting team arrived. If true that would mean those involved staggering through the airport with more than $5m - a little hard to do discreetly.

Mr Zulu is also perplexed about the disparate treatment of the men since their arrest.

Whistleblower

He says that while the Zambian and three other foreigners were sent to jail to await their day in court, the six Egyptians were put up in a guest house. Have, he suggested, VIPs in Cairo been leaning on the Zambian authorities?

The man who allegedly carried the bags of fake gold onto the plane has since turned whistleblower and is reported to be helping Zambian police get to the bottom of all this.

Over the last couple of days several more Zambian nationals have been arrested at a makeshift fake-gold processing plant, and more arrests may well follow.

As interest in the case around the world has grown, so has speculation.

A think-tank called the Egypt Technocrats, made up of independent Egyptian professionals living around the globe, claims there are more than 300 secret companies inside Egypt involved in money laundering operations.

Some say vast amounts of money may have been smuggled out of the country since President Abdel Fattah al-Sisi came to power nine years ago. If true, could this flight be just one of hundreds that have made similar trips?

The theory being advanced in some circles is that senior military officials and businessmen in Egypt, fearful that President Sisi's regime could collapse, have been desperately trying to get their money out of the country.

Though as with everything to do with this mysterious case, nobody can be sure how much of all this is true.

The hope is that when a trial finally takes place many of the questions raised will be answered.

The danger is, however, that it might just lead to even more questions.