The issue of WhatsApp's encrypted service, which is closed to anyone besides the sender and recipient, had come under criticism soon after the attack. "It's completely unacceptable. There should be no place for terrorists to hide. We need to make sure that organisations like WhatsApp, and there are plenty of others like that, don't provide a secret place for terrorists to communicate with each other," U.K. home secretary Amber Rudd had said.
Security sources say the message showed the victim's motive was military action in Muslim countries, while the article adds that though ISIS claimed responsibility for the attack, "no evidence has emerged to back this up."