Exhibit A

It's a fair bet that at least one day this week you read a newspaper story about an apparently loving normal, family torn apart by a multiple murder - committed by one of its own members.

The stories always seem to include a long shot of an ordinary suburban home in a quiet village somewhere turned into a crime scene; a studio photograph of the nuclear unit in happier times, beaming to the camera; and a lot of quotes from neighbours along the lines of: "He/she seemed such a nice, normal person, we never suspected a thing". Normally you read it, feel a pang of sympathy, turn the page and forget it. But Dom Rotheroe's ingenious and compelling thriller, which had its cinematic premiere at Raindance, takes this as the starting point to examine what turns everyday people into multiple murderers and challenges the audience to understand and even sympathise with someone driven to destroy the people they love best.

Rotheroe sets out his stall from the start. The opening shot is a page from a police log, stating that the exhibit of the title is camcorder footage taken by a teenage girl (Brittany Ashworth) in the weeks leading up to 'the murders'. At first she's excited by her new present. Dad (Bradley Cole) is a cuddly overgrown schoolboy; Mum (Angela Forrest) is hard-working and harassed but loving. The family home is a nice suburban semi but they're hoping to move on to somewhere a bit bigger and better on the back of Dad's prospective promotion.

Naturally there are a few clouds on the horizon - she's not too keen on her older brother (Oliver Lee) and she has a crush on the girl next door. But generally, this seems like the kind of family we all know, and the footage is the familiar mixture of jerky shots of barbecues and trips to the beach and the odd self-conscious 'video diary' piece. The tension - and poignancy - comes from the audience's awareness of the context and the certain knowledge that it's all bound to come apart.

If the words "Blair Witch Project" are on your lips at the moment, yes, there are similarities. But the screenplay was originally written in 1999, before Rotheroe was aware of Myrick and Sanchez's now-legendary horror effort. And, at heart, this is a very different film. The horror here comes not from classic horror tropes such as the woods and the dark, but the unconscious unfolding of a narrative that proves the worst demons lurk not in the realms of the supernatural but within ourselves. It unfolds subtly and gradually with the accretion of small details. Dad is spreading the family finances very thinly to fund the move to their dream home and when the crises begin to pile up his reaction is first to try disguising them with forced jollity, then to retreat even further into himself. The family's exasperation with him leads to a series of rows, in which long-buried secrets are exhumed and paraded. The camcorder is a constant mute witness, but someone's worked out how to use the night vision facility...

Exhibit A is not really a suspense thriller, in that you quickly realise who the eventual perpetrator is. The tension arises from the inevitability of the final act, and the fact that there is no authorial 'distance' from the central story. Every shot is from the camcorder, and the action rarely moves out of the family's house and back garden. You feel trapped, but also intimately involved with four characters who are all basically sympathetic but, in their own way, doomed. The performances are uniformly excellent. Put simply, you forget you are watching a fictional narrative for long stretches of the film, so completely do the actors inhabit their characters. Deliberately casting relatively unknown performers adds to the sense of reality, and to the audience's empathy, but if there's any justice this will be the springboard to bigger things for all of them.

Of course, there are moments when the central conceit becomes more obvious - there's certainly an editor's hand at work here, and the nausea-inducing jerkiness of the opening scenes (a problem shared with BWP) soon gives way to much more static, professional-looking takes. There are also (again, as in BWP) moments where you do question whether someone running or fighting for their life would actually still be able to work a camera - or even think to switch it on. But for the most part, disbelief is willingly and successfully suspended.

This is a gripping and moving film, which has something to say about the darker side of the YouTube world, where every minute of your life (warts and all) can be preserved and played back instantly. It also makes pertinent comments about the 'if you can't afford it, borrow' approach to home-owning and indeed everything else in our consumer-oriented society. One of the film's most telling images is of a hidden bin bag full to the brim with used lottery scratch cards. And the scenes where Dad is humiliated and undermined by amoral estate agents and aggressive unpaid builders are as harrowing as the horrors that eventually arrive.

The final scene is over-extended, it has to be said, particularly as by that time the audience is all too aware how things are going to turn out in this particular episode of 'to buy or not to buy'. Despite a short running time the conceit occasionally feels a little stretched. But on the whole it's a definite success that deserves a wider audience. There's no UK distribution deal at the moment, but there are plans for a DVD or possible internet release. And on TV it would blow most of those glossy, overwrought prime-time dramas clean out of the water.