The TV news told one version of Bloody Sunday, and Margo Harkin saw another. Now she's telling the families' side, writes Susan McKay

When the day came for Margo Harkin to give her evidence to the Bloody Sunday Inquiry, she was racked with anxiety. By chance she met Kay Duddy, whose brother, Jackie, was one of the 13 people murdered. "She said, 'Margo, you look terribly worried,' and I began to cry," says Harkin.

"She got out this hanky and I started to sob into it and then she told me it was Jackie's hanky and that I was to take strength from it." Jackie's hanky, still stained with his blood 35 years on, actually belonged to Edward Daly. It is the bloody white flag the then young priest is seen holding up in the now famous photograph. He was trying to lead to safety those carrying the body of the 17-year-old boy off the street where he was shot by British paratroopers on January 30th, 1972.

Jackie's hanky is now the subject of an academic thesis, and Bloody Sunday has been the subject of two inquiries (the most recent one lasting six years), numerous books, speeches, reports, documentaries, several plays and two feature films. Now Harkin has made a new documentary, Bloody Sunday - A Derry Diary, to be shown tonight on RTÉ.

Why? "Because I was there on the day and I remember the complete shock and horror of it," she says. "Because the aftermath of it taught me a huge lesson - that those who control the media control the truth. Because the Saville Inquiry has finally allowed us to describe what really happened. Because it has always been a story deep down inside me that I wanted to tell."

Harkin was born on the very ground on which the dead of Bloody Sunday fell. "My parents lived with my Granny in Pilot's Row in the old Bogside," she says. "I still feel very much part of that place."

When she was five, the now more prosperous family moved to the village of Drumahoe on the outskirts of Derry.

Drumahoe is the sort of place where pavements are painted red, white and blue. A local Orange Order band used to stop and play loudly at the gate. However, Harkin remembers some lovely people, and the happiness of city children (there were 16 children in the family) let loose in the country. She hated her seven years at convent boarding school. "It was like prison," she says.

IN 1970, SHE went to art college in Belfast. "They were the worst years to be in Belfast," she says. "There was constant rioting and disruption and murders and fear." She was engrossed in politics. "Like so many others, I took part in the civil rights marches and I went to debates at which Bernadette Devlin and Eamon McCann spoke. It was thrilling and inspiring and it felt like a revolution." Bloody Sunday changed everything.

"A faultline was established. Before that, we thought the Northern Irish state could be reformed. But to see that they did that, shooting down innocent people, and then covering it up, claiming they'd shot gunmen . . . I raced back to Belfast to tell people what I'd seen, but they didn't believe me. They believed what they heard on the news."

The Widgery report consolidated the lie. Hundreds of young Catholics across the North joined the IRA. Harkin says she couldn't. Although she was an atheist by then, the principle of "thou shalt not kill" was firmly embedded in her moral code. "But I can understand those who felt there was no longer any other way."

By this time, she had met the love of her life, Kevin O'Carroll. They married, and both got teaching jobs in Derry's Creggan estate. O'Carroll went on to become a leading light in the North's community development sector. Harkin got involved in the Derry Youth and Community Workshop. "The idea was to stimulate young people to get jobs," she says. "But there were no jobs. It was naive."

Then Art O'Briain, the director of the new Field Day theatre company, offered her a job on the legendary first production of Brian Friel's Translations. "It was just completely right for me," she says. She went on to secure a much-sought-after place on a design course in London.

In 1984, funded by Channel 4, Harkin and others set up the Derry Film and Video Collective. In 1990 Harkin co-wrote and directed Hush a Bye Baby. It was one of the first Irish feature films to deal frankly with contemporary life for young people and it won a string of awards around the world.

"It was a very raw wee film," she says. "It spoke of its time, of teenage pregnancy, the abortion debate, and supergrass trials." Her own company, Besom productions, has made documentaries and schools programmes.

When Tony Blair announced the Saville Inquiry in 1998, Harkin immediately set about finding funding to make A Derry Diary. It wasn't easy, but RTÉ's Kevin Dawson was interested. Eventually, RTÉ, the Irish Film Board, the NI Film and Television Commission and the German ZDF broadcaster all got involved. "I shot 180 hours of footage that had to be cut down to 85 minutes," she says. "I knew I needed an outside eye - my co-producer, Karl Ludwig Rettinger, was very influential in shaping the film."

IN SEPTEMBER 2005, O'Carroll had a sudden, massive heart attack and died. "I was devastated," Harkin says, tears flowing. "We had a profound love and the prolonged grief I've experienced has made me feel at times I was going to go mad."

A friend gave her Joan Didion's book, The Year of Magical Thinking, about the aftermath of the sudden death of her husband. "It is about trying to understand death at the same time as believing that the person will come back," says Harkin. "I learned from her that many suddenly bereaved people lose their businesses. I had to salvage my work. Our daughter, Kate, is at university, and she is the most important person in the world for me now."

Harkin is known as a prodigiously hard worker, and she points out that independent film-makers have no choice but to put in long hours. After O'Carroll's death, she worked day and night, taking on a documentary for the BBC about the 1981 hunger strikes as well. This got a huge audience when it was shown last year.

What was it like making films about death while in the throes of grief? "Family and friends were a rockbed of support, and the Bloody Sunday families were hugely supportive. It sharpened my understanding of what they had been forced to bear for all those years."

The film is powerfully revealing of the pain, the tenacity and the rage of the families. "A lot of people are very damaged," says Harkin. She shares the widespread disgust over the fortunes made by lawyers through the inquiry, which cost nearly £200 million. "But it had to be done. The families persisted and they do feel vindicated." Lord Saville's report is due next year.

Harkin's own evidence was controversial. She saw a gunman firing on the British. Few others saw this, and some don't believe he existed. "I saw him and I had to tell the truth," she says.

She's now working with Joel Conroy on a film about surfing, and is just back from California and Hawaii. "I've released myself," she says, smiling. "It was so sensual and beautiful, and so not about death."

Bloody Sunday - A Derry Diary is on RTÉ 1 tonight at 10.15pm