The Hundred-Winged Angel

As the famous 'Hundred-Winged Angel' melted in the cathedral fire, a human skeleton tumbled from its bronze shell, its bony fingers tightly clutching half of a silver locket. Inside the unburned hollow wings, police discovered 15 slips of paper. They all confessed to the exact same murder, yet each was written in a completely different handwriting. Records show the city's current Mayor generously donated this statue exactly 15 years ago. What is the truth behind the angel?