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?
It is technically impossible to detect illegal transactions for blockchain if you are sending your payment to another bitcoin address without any note or without using the API.
But if you are making API payment, then it can be proven that you have purchased some illegal things looking at the website. But in deepweb, your ass is hidden, so you can transact freely.