In 1999, I became obsessed with the JFK assassination. It started with one conspiracy book, and then another, and then another. The more I read, the hungrier I got. Within weeks, I was forcing friends to watch the Zapruder film with me. 'Look at that!' I would implore them. 'Tell me how that could be a shot from behind!'

As I continued my research, I became filled not just with the excitement of discovering dark forces at work behind the events of history (although that sort of paranoia is extremely pleasurable, even addictive) but also with a sense of civic responsibility. If a hidden cabal had struck down one of the great leaders of the US and delivered us to Vietnam and Nixon, it was imperative to expose that cabal. I decided to apply my abilities and experience as a film maker to this new purpose.

I was just One Man up against The Conspiracy. I felt humbled and small while at the same time my life took on a new significance. I mattered.

Oh, and I should add: I was completely wrong.

The very obsession that led me to be consumed by the JFK assassination ultimately led me to the boring truth: There was most likely no conspiracy to assassinate President Kennedy. As I checked out each of the tantalising theories that were keeping me up at night, I found that they began to wilt on examination.

I could go on and on in detail about these theories, but I've lost enough friends already. Gallup polls consistently show that up to 80 per cent of Americans believe there was a conspiracy to assassinate JFK. The handful of us who have actually looked into the matter enough to reach an informed conclusion can only shake our heads in wonder at this statistic.

All of this is to set the scene for my encounter with another sexy theory: That Jesus Christ never existed.

Crazy, isn't it? We all know that there was at least an itinerant preacher who walked around Palestine in the first century ' the only dispute is whether he was really the son of God or just some raving madman, right?

That's what I thought, too. And when I encountered this strange idea that Jesus never existed at all, I was sure I had stumbled into similar territory that had temporarily claimed my gullible mind with the JFK nonsense. Still, I was curious. What kind of person, I wondered, does it take to believe and propagate such an obviously false idea?

But then I looked at the evidence. And unlike the JFK theories, the theory that Jesus Christ never existed actually holds up under scrutiny. In fact, as the pieces fit together, they made me wonder why I ever thought Jesus did exist.

The basic story believed by most Christians is that disciples of Jesus ' eyewitnesses to his actions ' wrote the Gospels, and then those Gospels were used by early Christians, such as Paul, to spread the word of Jesus throughout the known world.

Somehow in my own personal transition from fundamentalist Christian to atheist (long story), I had retained this belief myself. I thought that by rejecting the supernatural elements of the Jesus tale I had rejected the falseness of it. But I had fallen into a trap that literalist Christianity has used with astonishing effectiveness for centuries to shield itself from inquiry.

Reading the work of scholars such as G A Wells, Robert M Price and Earl Doherty, I discovered that the first-century chronology I had internalised was indisputably false. Contrary to the impression given by the order of books in the New Testament, the Gospels came after Paul's letters. Paul's letters, in fact, largely represent the beginnings of Christianity. The Gospels represent Phase 2.

And Paul seems to have had no idea that Jesus existed as a real human person.

This fact is so simple that it is easy to miss how it devastates the premise of a major world religion. But it does. For forty years, at the least, Christianity existed without any Christians apparently believing in a human founder. These early Christians write of a Christ who existed purely in an upper, spiritual realm. And his only actions were dying on a cross and rising to his father ' pretty much like the figureheads of a handful of other saviour religions of the period.

Early Christianity was simply a Jewish version of older cults that were also built around mythical saviour figures ' Osiris, Dionysis, Mithras and many others. In fact, the name Jesus simply means 'one who saves'. Not only was Jesus just another saviour god, he was a generic one.

If you were to tell Paul or other early Christians the story of Jesus, they'd have looked at you like you were crazy (which, yes, would have been deeply ironic). Paul writes 80,000 words about Christianity, but here's what he never mentions: Mary, Joseph, shepherds, the star, Bethlehem, wise men, young Jesus teaching in the temple, water into wine, healing the sick, raising Lazarus, any miracles at all, the sermon on the mount, Jesus ever saying anything at all, Jesus betrayed by a disciple-well, you get the idea. This 'history' didn't exist until someone else made it up later.

It apparently took decades before the early Christ cult felt the need to create more detailed allegorical literature about their mythical hero ' that is, the Gospels, which if read without bias suddenly look like they couldn't possibly be anything but fantastical stories created out of the Old Testament and other myths in circulation at the time. And it was much later that the Roman church assembled a version of the Jesus tale (from many competing versions) and decreed it literally true.

As I researched these areas and created my new film The God Who Wasn't There, I was struck both by how obvious it was that Jesus probably never existed and by how skittish some of those familiar with the evidence were to publicly acknowledge it. Like the fact that the Earth revolves around the Sun once was, the fact that Jesus appears to be entirely mythical is an uncomfortable truth for Christianity. And in the US especially, anything that makes Christianity uncomfortable is considered 'intolerant'.

So The God Who Wasn't There won't be playing anytime soon through mainstream channels. Fortunately, however, independent film making and digital technology have reached a point where even if the main gatekeepers say no, there are still ways to get one's message out. As I like to say when I speak at film festivals, it's not easy, but it's possible.

With The God Who Wasn't There, we're trying a simple, experimental new strategy. The DVD is on sale at the film's website, thegodmovie.com, but anyone who buys the DVD also gets the right to screen it publicly ' for paid admission ' without paying the makers a dime. It's the only movie I know of that comes with theatrical screening rights as part of the purchase price.

So far, the strategy is working. Humanist, atheist and other freethought groups have been holding screenings as fundraisers not only in blue areas of the United States like San Francisco and New York, but also in the heart of the Bible-belt states like Alabama, Georgia and Indiana. Local press reports on the screenings, local Christian leaders react angrily, and suddenly the idea that Jesus never existed is on the local TV news in Birmingham, Alabama.

And that's really the point of making and distributing the movie. Many Christians react angrily to the idea that Jesus never existed because they instantly recognise, at a deep level, that it could be true. Upon scanning their memory for a reason that Jesus must have existed, they realise that they don't have one. It is a blow to their faith, a small victory for doubt.

I think these kinds of small injuries to religious faith will play an important role in eradicating it. Want to help? Get the DVD. And then make a stink.

Brian Flemming is a film maker and writer.