If the content of WeChat involves criminal cases, especially the investigation clues of important criminal cases, the public security organs at or above the county level may take technical investigation measures against the mobile phone number. This method can track the location of your mobile phone, even if it is turned off, it can track and monitor your phone and intercept your WeChat.
Within a certain period of time before the technical investigation means is started, your calls and WeChat content will be saved to the computer of a company providing communication services, regardless of receiving and sending.