We arrived at Potosi bus station and were in the process of unloading our backpacks from the roof when an elderly gentlmen came up and shook me vigourously by the jacket. I had one backpack on and the other between my feet. This gentleman obviously had an accomplice who lifted the backpack from between my legs. He ran off through a crowded market before I could react. The other gentleman disappeared immediately. The whole operation was very professional, and other travellers had also had their bags taken. I lodged an official report at the Potosi Tourism Police Station but they advised me it was very unlikely the bag would be recovered and gave me an official police report.