The United States government is running MS-13 criminal investigation. Thus, US government urged Facebook to break its end-to-end encryption on Facebook's Messenger app to keep surveillance over Facebook.

As per reports, Facebook has not agreed with the request received from US Government.

The Department of Justice argued in court that Facebook should be held in contempt for failing to comply with the government's request. Facebook defended itself saying in order to comply, it would have to completely remove encryption from Messenger for all users.

Facebook Messenger is not encrypted end-to-end for normal conversations. Though, there is a Secret Conversation feature that allows all messages between two people to be secured where not even Facebook could decrypt it in transit. US government has alleged that their MS-13 suspect is taking advantage of that  Facebook feature to communicate.