By Rageh Omaar
The Shroud of Turin, BBC Two
The Shroud Center of Colorado depicts a burial configuration
There are very few Christian relics as important and as controversial as the Shroud of Turin.
This linen cloth, measuring about 4.4m by 1.1m (14.4x3.6 feet) holds the concealed image of a man bearing all the signs of crucifixion.
Scientific tests have proved that there are blood stains around the marks consistent with a crown of thorns and a puncture from a lance to the side.
In a new documentary, we have been given intimate access that no other broadcaster has had before.
Until the 1980s, millions of Christians around the world believed the Shroud to be the burial cloth of Christ.
Put simply, it meant that for millions of people the Shroud was, in effect, a Polaroid of Jesus' death - a snapshot of the defining moment in Christianity. It put the Shroud in a league of its own in the realm of the most important Christian relics.
But in 1989, the significance of the Shroud seemed to evaporate after a radiocarbon dating test pronounced a stunning verdict - the Shroud of Turin was indisputably a medieval fake.
With that judgement the extraordinary story of the Shroud of Turin fell out of the public imagination.
After all, how could any other kind of evidence about the shroud compare to the verdict of science?
Rageh Omaar talks to scientists who have long studied the Shroud
But the amazing story of the Shroud of Turin has simply refused to fade into obscurity and die, for the simple reason that a conflict of evidence has emerged which is about to re-ignite the debate around this compelling religious artefact.
If it is a medieval forgery, then how was this image made? So far, no one has been able to explain it. And from this simple question tumble a multitude of other questions.
My quest took me to three continents, from the US, to Italy, to Jerusalem and the radiocarbon dating laboratory in Oxford, which was part of the original test 20 years ago.
In the film I interview John Jackson who led a major investigation on the shroud in 1978 and has made the study of the Shroud his life's work.
Mr Jackson, a lecturer in physics and cosmology, introduced me to a wealth of fresh historical and forensic evidence that linked the Shroud of Turin to two earlier Shrouds of Christ.
The first was in Constantinople and mysteriously disappeared in the sack of the city in the Fourth Crusade in 1204. The second is, of course, the Shroud referred to in the Gospels.
Looking for 'coherence'
The irresistible force of science seems to have hit an immovable object. The mysterious image of a crucified man has refused to lie down and die.
The new evidence raises a question mark over that carbon-14 verdict. Should the margin of error have been wider? Could the image on the Shroud have been forged earlier in time?
Mr Jackson has developed a new hypothesis that could explain how a genuinely ancient piece of linen could produce a distorted younger date. I took this to Professor Christopher Ramsey, director of the Oxford Radiocarbon Accelerator Unit.
The real artefact is kept at the Cathedral of Turin
He agreed to collaborate with Mr Jackson in testing a series of linen samples that could determine if the case for the Shroud's authenticity could be re-opened.
"With the radiocarbon measurements and with all of the other evidence which we have about the Shroud, there does seem to be a conflict in the interpretation of the different evidence," Professor Ramsey tells the BBC.
"And for that reason I think that everyone who has worked in this area, radiocarbon scientists and all of the other experts, need to have a critical look at the evidence that they've come up with in order for us to try to work out some kind of a coherent story that fits and tells us the truth of the history of this intriguing cloth."
The Shroud of Turin will be broadcast on Saturday, 22 March at 2030 GMT on BBC Two