In 2005, Sally Anne Bowman, an 18-year-old model, was stabbed to death and sexually assaulted outside her south London home. Her boyfriend had dropped her there after an argument. But he wasn't her killer -- his DNA didn't match that found at the scene.
A media appeal for help produced no suspect. Neither did a voluntary DNA-screening programme in the area. Instead, a brawl the next summer outside a local pub showing World Cup football led to an arrest and a chance DNA match that caught the killer.
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