I'd like to know how the criminals got away with the ransom. Did they use a mixer, or what? Even if they did, it should be possible to find, at least, the IP address they used in the transaction to the mixer.
IP can be masked pretty easily, with plenty of tools, so it's a bit pointless to know it, they can even do it via mobile and attach their phone to a wifi with some sort of a proxy, then change location
you don't even need a mixer in that case, they may force you to split the stolen sum into multiple addresses