Now with the two cards both in Tenth Edition together, you can see how close the connection was. The victim in the art of Assassinate was designed to represent a victim of Mark Zug's Eighth Edition Royal Assassin in particular.
Note how, in Assassinate's art, the black ichor dripping from the victim's mouth and leaking into his eye socket resembles Royal Assassin's identity-obscuring makeup. And the dagger stabbed into the victim's gut is the same as the one that Royal Assassin is drawing from under his cloak.
Assassinate art by Kev Walker
Royal Assassin art by Mark Zug