Authorities have expanded a probe into possible insider trading at China’s largest brokerage, Citic Securities, to include Cheng Boming, president and chairman of the firm’s international division, The Wall Street Journal reported, citing a statement from the company. A report from state news agency Xinhua said Cheng was suspected by police of leaking and trading on unspecified inside information, as were two other members of the firm who have senior operational roles. As the brokerage arm of China International Trust and Investment, the government’s best-known financial group, Citic Securities has faced heavy pressure in the wake of the mainland’s equity market collapse.