https://www.cnbc.com/2019/02/05/facebook-messenger-will-now-let-anyone-unsend-messages.html

Facebook Messenger now gives anyone the option to delete a regretful or mistaken message from their chat history.

Facebook initially promised the feature after TechCrunch reported in April that multiple people said Facebook messages they received from CEO Mark Zuckerberg later appeared to have been deleted while their own messages remained. At the time, Facebook told TechCrunch Zuckerberg's messages were deleted for security purposes.