Re: @ Dan 55
You're asking for something different. According to the quote, they wanted a message:
"British security sources last month revealed Masood sent a WhatsApp message but it could not be accessed because it was encrypted by the popular messaging service"
WhatsApp deletes messages once received by the client. The police would need to look at to the sender or the receiver's phone because WhatsApp don't keep a message history.
I don't know how WhatsApp holds contact lists or logs IP addresses/geo-location so I didn't comment on that.