The head of a Chinese exchange that trades minor metals was captured by angry investors in a dawn raid and turned over to Shanghai police, as the investors attempted to force the authorities to investigate why their funds have been frozen.

Investors have been protesting for weeks after the Fanya Metals Exchange in July ceased making payments on financial investment products. The exchange, based in the southwestern city of Kunming, bought and stockpiled minor metals such as indium and bismuth, while also offering high interest, highly-liquid investment products from its offices in Shanghai and its financing branch in Kunming.

Troubles at the exchange are one of many factors contributing to turbulence in China’s financial markets, as a slowing economy exposes the weaknesses of the country’s debt-driven growth.