Murderous Crawling claws are the severed hands of murderers animated by dark magic so that they can go on killing. Wizards and warlocks of a dark bent use Murderous Crawling Claws to avenge their deaths with the claw created in advance of their death and activated upon it, continuing their persistent trek until either their own demise or their target's.  Should a group be responsible, each member of the group will be targeted individually until this condition is met.  Focusing on one target at a time. 

Should a Murderous Crawling Claw succeed in its mission, its spirit is then freed to choose its own targets allowing the murderer to live on through the hand.  

How they come to be.  Through dark necromantic rituals, the life force of a murderer is bound to its severed hand, haunting and animating it to be a Crawling Claw.  Sometimes the ritual invoked to create a Crawling Claw goes much better than the caster intended resulting in a Murderous Crawling Claw.  (DM choice, Natural 20 default) The ritual must start within 3 days from the time the hand is severed from a murderer for this potential result.

To this end, ritualists and their servants frequent public executions to gain possession of suitable hands, or make bargains with assassins and torturers. A murderer may even seek out a caster of such a ritual for the chance at this freedom in death seeing no escape from his demise through contacts the offering of grand treasures.

Undead Nature. A crawling claw doesn’t require air, food, drink, or sleep.