Dorothy Byrne: Why we decided that the footage had to be shown

The bodies of naked women are thrown and dragged on to the back of a truck. As each woman is pulled aboard, soldiers make crude remarks and laugh. Elsewhere, other soldiers film themselves laughing at the bodies of dead, bound women who appear to have been raped before they were murdered. In other mobile phone footage, a woman kneels as instructions are given as to how to execute her. Then her brains are blown out.

This is just some of the footage we will be showing in Sri Lanka's Killing Fields on Tuesday night. I never thought I would see sequences like these, showing the mutilation, murder and degradation of women, on British television. I don't urge you to watch this programme. It's horrific. The images will remain in your mind, maybe for years. I can't get them out of my head. The programme goes out at 11pm and the worst images appear in the last part – several hours past the watershed which protects children. But there are probably many adults who shouldn't watch; people who can't watch horrible stuff on the news. I would rather I had never seen it.

We shouldn't have to show this film at all: a UN panel has already said there is strong evidence that war crimes and crimes against humanity were carried out by the government during and in the aftermath of Sri Lanka's civil war. They believe that up to 40,000 innocent civilians were killed. That panel of experts called for a major war crimes investigation. Nothing has happened. The Sri Lankan government didn't allow journalists or UN personnel to see what happened but both Tamils and government forces filmed themselves, often on mobile phones. It is this footage we show.

The video which appears to have been taken on phones by soldiers themselves is the most grisly. They film and photograph themselves executing prisoners. There is film, and hundreds of photographs, of the dead lying in pits or in long rows. Many are bound and many have shots to the head; these do not appear to be the victims of shelling or other forms of "legal" warfare. A small group of children lie in a pit. Prisoners are shown alive, some- times being taunted, and then dead.

The Tamil footage is at moments even more harrowing. There is strong evidence hospitals and refugees were deliberately targeted.

The Sri Lankan government has claimed the footage of the executions and the aftermath of killings is fake. Not what the forensic pathologists and video experts say. The Sri Lankan government rightly say the Tamil Tigers killed people. Yes they did, but they didn't kill 40,000 civilians. Some other force did that and all the evidence is that the murder was systemic.

It's not for us to tell you what to think. Watch yourself and judge. It makes you think there should be some international body that holds people to account for atrocities like that. Wait a minute, there is.

Dorothy Byrne is Channel 4's head of news and current affairs