It looks like my theory about it being FreeBitco.in that made this transaction was proven correct. Somebody posted this withdrawal transaction on their thread:


Following the largest output, which is most likely the change address, leads to bc1qfdh66p7vdlc4qhk9f52z89v62yq8hy28qku7h2. That address then makes a payment in the transaction 9536d1fc01a9c2ecedce0c8267b15b755ce8348838bd4dacc4ef7f07ce44afd4, which also includes three inputs from address 3DpHxqfmiFtyykdGhYcVcKnJGodUgkd2A4. This was one of the addresses used in the payment which sent 2.6 BTC to Satoshi.