Murdercube seems to be down. Judging by the thread over at 4chan, its been down for a several days.
Here is a link to get magnet link for the ar/k/ circa 2016.
https://pastebin.com/uF0NV5Nf
I checked it, it is being seeded.
A backup of murdercube can be found here: https://the-eye.eu/public/murdercube.com/
This is an information sharing thread I guess.