A picture of sisters at Beslan became the unlikely inspiration for the new dance piece from Rex Levitates, writes Belinda McKeon

It was a day of unimaginable horror. Parents and children who had gathered in a school gymnasium for the celebration known as the "Day of Knowledge" - the first day of September, and of the new school year - found themselves taken hostage in a siege that ended in over three hundred deaths. The images of Beslan seared themselves into the minds of all those who encountered them. But so terrible were the stories told by those images that, for many, the instinct was to shy from the full reality of the tragedy, to close eyes and ears to the truth of what had occurred.

Liz Roche, the choreographer and dancer who forms one half of the Dublin-based company Rex Levitates, was among those who felt the guilty urge to turn away. "I think it was one of those things that was just so horrendous that it was almost hard to think about it," she says. "One of those things that you couldn't let in, or else you wouldn't go anywhere or let anything happen. More than anything, actually, I remember my mother's reaction. Because sometimes I can be a bit disconnected, it's like I don't get things for a while, but she lost it. And it was when she said something about my nephew, imagine him going to school and not coming back, that . . . "

She catches her breath sharply, imitating herself at that moment when distant atrocity became deeply personal. "And I suppose I needed that."

Liz Roche didn't realise it at the time, but one image of the Beslan siege was about to become personal in an even more immediate sense for herself and her sister Jenny, her partner and collaborator in Rex Levitates. Excited and inspired by the work of the acclaimed British choreographer Rosemary Butcher, the two had commissioned her to create a piece of work with them. Jenny had studied with Butcher at the University of Limerick, where she had been doing her MA in Dance; Liz had chosen Butcher as a mentor for her solo piece Gasp, performed in Dublin as part of the 2002 International Dance Festival, which grew into the larger piece, Resuscitate, commissioned for the same festival in 2004.

Both sisters wanted Butcher on board for their next piece, but what form that piece would take would be up to her. Butcher remembers that, at first, she had no idea what that form might be either. "I don't do commissions usually," she explains. "But I said yes. And then I saw this picture. I had been at home when the siege was on, watching what seemed like nothing escalate into this tragedy. And then I saw the front page of the newspaper."

The picture was of two sisters, their heads pressed together in disbelief and confusion, their eyes stilled by fear, fixed on the site of their children's suffering; they stood outside the school, waiting for news. And from their faces it was clear that the news was unlikely to be good.

"Veils over their heads, their cheeks together, the rain and the glass," recalls Butcher. "It just caught. And I immediately thought of Liz and Jenny."

Around the same time, Liz Roche was boarding a flight home from Paris, and deciding that it was time to make the phone call which had been put on the long finger for too long. Had Butcher made any progress with the commission? "I rang her - it was one of those 'do it now in case anything happens to the plane' moments," laughs Roche. "And she said, 'I've just been thinking about you. I've seen this image, of these two sisters, and it's perfect. You guys are sisters, and this is going to be the piece. But I need it to be something really different for me'." "Something really different for me" - coming from Butcher, a choreographer known as one of the most innovative in her field, this statement was nothing if not attention-grabbing.

Since she spent a number of years training in New York in the early 1970s, when she came into contact with the choreographer and film-maker Yvonne Rainer and the radical Judson Group, Butcher's work has been marked by its flight between art forms and the ease with which it negotiates concepts of movement, space and presence. Her early preoccupation with the postmodern movement has developed into a fluency and fluidity which has influenced whole generations of choreographers and performers. Everything she has done, from her landmark debut concert at the Serpentine Gallery in 1976 up to her most recent works, Still-Slow-Divided and White, has been passionately, confidently different. How much more different did she intend, with this Beslan-inspired project, to be?

Its form soon emerged. It would merge the filmed performance of the Roche sisters with narration by the cult American poet Robert Lax and a private score for each sister, developed through a process of delving into personal memories and using them as a secret basis for the creation of movement. Though they were wary about the idea of film rather than live performance, the sisters readily agreed. All that the audience would see of them in the sense of a live presence would be their seated or standing forms, looking at their own images on the screen. Butcher explains the thinking behind this first idea.

"The process I had in mind was that I wouldn't tell them what the event that inspired me was," she says. "And even though they knew, of course, that it was Beslan, still it was the image relating to the event, rather than the event, that was important. You know, looking at this image of the two women, that they are looking at something quite terrible. But until you read the caption, you wouldn't know what it was. What I was interested in was the idea of them looking at something and us looking at them looking."

This notion of an image within an image sent Butcher naturally to the film camera. "I was initially interested in making it completely as a film, which they were watching, to give us this idea of the frame and looking out through the frame. But then I saw them dancing live, and it was very strong. And I didn't want to lose that." The finished piece, then, combines recorded and live motion.

The rehearsal process for the piece has involved much more than just stretching and lifting for the Roche sisters. Butcher asked them to uncover, and to treat, their memories of childhood and of growing up, in a process which Liz Roche describes as deeply emotional; getting in touch with the complexity of emotion displayed on the Beslan sisters faces required the Roche sisters to go into moments of fear, bewilderment and grief in their own lives.

There were, she says, times when she didn't want to go anywhere near the place to which a particular memory wanted to bring her. But that discomfort was all part of Butcher's plan.

"Because they have a shared childhood, and because their lives have been shared to an extent, there is immediately something that holds it together. If I'd done it with two different people or two strangers, it wouldn't have that quality."

Each sister, she explains, works from a score that they have written themselves, consisting of symbols representative of particular memories which they have brought to the surface. Each performs from a private language, with private reactions. Does Butcher worry about the problem of communicating this hidden language to the audience in a meaningful way? Not at all, she insists; not with these sisters on board.

"They have these wonderfully expressive faces," she explains. "And I think right from the beginning this is very prominent, for me. They're very silent faces but they're extremely poignant in the little things that they do. And they're not expressions, in fact, there are no facial expressions really. But what's going on in their mind makes them look . . . " She runs out of expressions herself at this point; how the Roche sisters will look in Six Frames is for the audience to experience at first-hand.

Jenny Roche believes that the piece creates a space for the audience to come to terms with its own emotions and reactions to these two sets of sisters and their inner lives - but in ways that a more crudely story-driven piece could not facilitate. "In the past I would have thought of myself as a very emotional performer and dancer," she says. "And in the past few years I have been trying not to go there any more, because I feel that it doesn't allow creativity or distance or something new too come out. When dealing with a subject like this, I think when you go into the emotion of it, it doesn't allow anyone else in the space to have a response."

Don't expect wailing and lamentation from Six Frames, then. "I think if the performer was there crying and experiencing something, nobody else could - that's not good," she says. "So I think by trying to be, not distant, but present as much as possible, but to have that kind of neutral space, to be okay in it, and not to be falling apart in front of people, I think that gives them the space to have that experience."

"I think it's a poetic response to a real event," says Liz. "We spoke about this idea of how, in homeopathy, if you distill something it becomes much stronger. There's no recognisable element of Beslan in this piece. The idea has been to distill the piece as far away from the actual reality as possible to see if it hits on a deeper level."

Has it hit the duo on a deeper level, in terms of their relationship to, their knowledge of, one another - as sisters as well as as business partners? "I don't think it's possible to learn any more about each other," laughs Jenny.

"It was actually really lovely to do it. It's really nice when someone outside of that relationship manages that and works with it. It allowed us to enjoy that we have a really nice vibe, working together. When we're running the company it's always much more fraught because there's more pressure and responsibility. Not that the artistic experience was easy, but when someone comes in and creates a structure for you, an environment, then we can just kind of enjoy and look after each other."

Jenny speaks with feeling on this; at the genesis of Six Frames, she was recovering from an illness that left her physically exhausted, her body almost a stranger to her; Liz, meanwhile, was suffering from an injured back. The experience of pain and vulnerability, though in no way comparable to that which inspired their piece, rendered them a little closer to the wavelength upon which they had to create and perform. "Being with someone you trust, you know, it helps," says Jenny. "You can do this, you can get through this. You know that."

Six Frames - Memories of Two Women runs at Project Upstairs, Tues-Sat