According to some resources the recent ransomware attackers have already exchanged their Bitcoin for cash, but by first passing their Bitcoins through a mixer which made it tough to know the source. Mixers can largely help in hiding any Bitcoin transactions that too easily. But according to another resource, the use of Bitcoin in illegal activities have reduced to half and people have started using other cryptocurrencies for the same.
A few major mixers, including Bitmixer.io have alluded to being aware that a large part of their clients were from dark markets or involved in illegal activities. However, what is apparent is that intelligence software used by law enforcement has caught up and is still able to track users even with the long trail of mixing. It was precisely Bitcoin use that led to recent captures, despite using mixers. It's worth to note that few mixers have updated their techniques.
what mixers are they using, now that Bitmixer.io is closed?
There's a major, new player, whose ads you'll find plastered prominently in this forum. I also happen to be a supporter, as you can see. The admin reported a huge surge of new clients immediately after Bitmixer's closure. I'm sure the other mixers saw increased traffic as well.