We reveal how the power of forensic science not only found a killer but also freed an innocent man. Forensic evidence is a powerful tool - so powerful that if it?s misinterpreted, it can lead to a serious miscarriage of justice. That happened in the first story in this programme, where there was a chance the wrong person had been convicted of murder. Getting to the truth needed clear thinking and a remarkable scientific experiment. The programme also uncovers how an expert in facial comparison helped identify the suspects in a shooting at a Leeds nightclub. Experts reckon there are over five million CCTV cameras in the UK, all around our streets, businesses and homes. That?s one camera for every 13 citizens or so, recording footage 24/7. But spotting someone on CCTV who you think is your suspect is one thing, while actually proving it?s them is a very different matter. And that?s where detectives call for an expert witness.