Interception of WhatsApp messages, FBI successfully caught two suspects-WhatsApp,FBI-IT information

Bloomberg reported that Belgium law enforcement authorities on Monday arrested two suspected terrorists in a joint RAID, arrest warrants were issued to three others. Belgium said it and United States authorities to monitor suspect communications on WhatsApp. WhatsApp and its parent company, Facebook declined to comment. So the question is: WhatsApp cooperate with United States authorities monitor or a United States WhatsApp encryption system was cracked?

WhatsApp began in November last year to enable end-to-end encryption, WhatsApp is theoretically able to read communications. But it was not clear if encryption is being used by terrorists, because not all WhatsApp version supports end-to-end encryption, such as iOS versions are supported. Even if the content is encrypted, NSA or FBI could still gather meta data to understand network between the suspects. Analysis on WhatsApp encryption scheme, crack encrypted data is not impossible in theory, because the key is derived from the user's password.