Well as we all know that whenever we transact it always go through blockchain first. So is it possible that blockchain can detect illegal trasanction such as buying drugs, guns, hitman etc., especially on deepweb. And where does bitcoin go when blockchain detects a illegal transaction?
There are companies that do aim at detecting and monitoring illicit transactions in bitcoin for use by law enforcement, governments and merchants. For examples
https://www.elliptic.co/http://www.coinalytics.co/http://sabr.io/An they can do this because bitcoin is not anonymous, but only pseduo-anonymous.