Alibaba Group’s sprawling campus has collegial workspaces, laid-back coffee bars and, on the landscaped grounds, a police outpost. Employees use the office to report suspected crimes to the police, people familiar with the operation told The Wall Street Journal. Police also use it to request data from Alibaba for their own investigations, tapping into the trove of information the tech giant collects through its e-commerce and financial-payment networks. In one case, the police wanted to find out who had posted content related to terrorism, said a former Alibaba employee. “They came to me and asked me for the user ID and information,” he recalled. He turned it over. The Chinese government is building one of the world’s most sophisticated, high-tech systems to keep watch over its citizens. Companies including Alibaba, Tencent and Baidu are required to help China’s government hunt down criminal suspects and silence political dissent. Their technology is also being used to create cities wired for surveillance.