Chinese police probing the massive stock market crash that wiped about 3.2 trillion dollars of capital out of the market today claimed to have found clues pointing to certain trading firms suspected of manipulating futures trading. State-run Xinhua news agency reported, the team is currently carrying out further probes.It did not provide other details. After China's key stock index plunged by over 30 per cent from its June 12 peak, the government has stepped in with various measures to stabilise the market, including pouring in funds and restricting futures trading on a major small-cap index.