Three men have been cleared of trying to procure the raw ingredients for a "dirty bomb" which the prosecution claimed could have devastated a British city if it fell into the hands of terrorists. But mystery surrounds the material at the centre of the plot. So what exactly is red mercury?
By Chris Summers
If real, a red mercury bomb might cause radioactive devastation
The most bizarre aspect of the trial of Abdurahman Kanyare and his two co-defendants was the fact that no-one in the court could be certain whether the terrifying substance on which the entire prosecution case was based actually existed.
The prosecutor, Mark Ellison, admitted the police had no idea if there even was such a thing as red mercury - supposedly the main ingredient for a "dirty bomb" which could have devastated London.
But he told the jury at the outset: "The Crown's position is that whether red mercury does or does not exist is irrelevant."
He warned the jury not to get "hung up" on whether red mercury actually existed at all.
Mr Ellison said the fact was that the three defendants had hit upon a meaning for it as a substance which was highly dangerous and expensive, and they pursued it.
The indictment accused them of "conspiring together and with persons unknown to possess and article, namely a highly dangerous mercury-based substance, in circumstances which gave rise to a reasonable suspicion that it was to be possessed for a purpose connected with the commission, preparation or instigation of an act of terrorism."
It emerged during the trial at the Old Bailey that red mercury was something of an urban myth, a substance which was either radioactive or toxic or neither, depending on who you spoke to.
Indeed some of the conversations between undercover reporter Mazher Mahmood and the prospective buyers were bordering on the farcical.
At one meeting in a shopping arcade in Edgware, north London both sides kept asking what it was that they thought the other side was there to buy or sell.
Mahmood kept repeating, probably for the sake of his covert recordings: "Now let's just make it clear what exactly it is you want to buy."
Kanyare replied: "You know what we're here for."
When he gave evidence Kanyare said he believed red mercury was a liquid which could be used to wash soiled money.
Summing up, The Recorder of London, Judge Peter Beaumont, said: "He (Kanyare) told you that Muslim people from the Middle East are usually on the lookout for red mercury as a medicine, I thought he said for impotency but the other barristers thought he said it was for long life. Whatever it was, he said it was a faith medicine."
Kanyare testified that he had absolutely no interest in procuring a radioactive or toxic substance and would have had no means of testing it anyway.
The trial heard that when detectives checked Dominick Martins' computer after his arrest they found evidence that he had been scouring the internet trying to find out about red mercury.
He was particularly interested by an article, by Dr Anne Marie Helmenstine, which was posted on the About.com website.
The article aired the various theories about what red mercury is without confirming whether or not it really existed at all.
The five main theories are:
That red mercury is a reference to cinnabar, a naturally-occurring mercuric sulphide. The red pigment derived from cinnabar is known as vermillion.
That it is a reference to the alpha crystalline form of mercury iodide, which changes to a yellow colour at very high temperatures.
That it is simply referring to any mercury compound originating from the former Soviet Union. The 'red' tag would simply be a legacy of the Cold War era.
That it is a ballotechnic mercury compound which just happens to be red in colour. Ballotechnics are substances which react very energetically when subjected to shock compression at high pressure. They include mercury antimony oxide which, according to some reports, is a cherry red semi-liquid produced in Russian nuclear reactors. This theory contends that it is so explosive that a fusion reaction - a nuclear explosion - can be triggered even without fissionable material such as uranium.
That it is a military codeword for a new nuclear material, probably manufactured in Russia.
Interestingly Dr Helmenstine mentioned rumours of prices of up to $300,000 being charged on the black market for a kilogram of red mercury.
But is there any way of knowing if red mercury really did exist?
No bigger than a baseball
In the early 1990s, in the wake of the collapse of the Soviet Union, several articles were published claiming that a pure fusion device had been invented.
It reportedly weighed around 10 pounds and was no bigger than a baseball.
If such a device existed, and was capable of triggering a nuclear explosion, the threat to the world - especially the western world - would be catastrophic.
But no such bomb has been discovered and nobody - not even Osama bin Laden from his mountain base in Afghanistan or Pakistan - has even threatened to use one.
So is red mercury just a hoax?
Let us hope so.