Documents reviewed by Rest of World show several companies backed by U.S. tech giants provided policing or censorship tools to Chinese law enforcement.

• Two of the companies were selling censorship software or working with the police before they joined Microsoft’s long-running incubator program.
• The vast majority of Chinese participants don’t have surveillance applications, and some programs were launched in a friendlier era in U.S.-China relations.
• Startups’ technology can combat phone scams and find missing children, but software has also played a role in online censorship and surveilling populations.