Transactions with bitcoin leaves no mark behind it. That's the biggest advantage of bitcoin. But unfortunatelly, people too that advantage and used it in the wrong ways. Deep web business is now done with bitcoin because they are totally safe and no one can track them. It's very unfortunate to see these kind of criminal activities affect people's opinion towards bitcoin. This needs to change by spreading knowledge about bitcoin.
What do you mean by "Transactions with bitcoin leaves no mark behind it"? As far as I know, every transactions in Bitcoin is recorded and can be traced since it was written on a ledger. The only thing that cannot be traced is whom the Bitcoin wallet or account is connected since the identity of the owner of the wallet is anonymous except those who declared it through local bitcoin wallet or exchange.