According to security officials, the Prime Minister is attempting something she's never done before: trying to force whatsapp to decrypt messages belonging to Khalil Masood, the parliament attacker.
Sec officials say that Masood apparently sent a message just before he left his hotel to attack Parliament Square. Officials want to know who that message was to, what it said, and whether or not they knew of the crime.
One expert says that if the individual is discovered to have known of the attack or been an accomplice.
He or she can be charged as an accessory to a terrorism related crime for not simply reporting the manner to the appropriate officials.