There are six books to collect:
Arkay the Enemy
Legions of the Dead
Corpse Preparation volumes I-III
N'gasta! K'vata! K'vakis!
Reading these will begin the path to necromancy.
There are a few more requirements:
having at least 50% in both conjuration and alchemy
learning at least 3 of the summon undead purchasable spells

Meeting these requirements will then trigger an event that then allows a character to start collecting corpse containers.

Also, the six books will also be stuffed with notes once this event happens. A character will need to seek out multiple copies to collect the notes. The notes will explain the facets of necromancy, and the final note will complete the sequence that will allow characters to kill NPCs and use their corpse! There are 12 notes total.

All rituals only work between 12am-1am.

Functions currently available:
collect corpse containers
carry corpses
arrange corpse for ritual
*create vessels for animation
animate undead
learn 'blood ritual', this allows characters to collect the corpse of an NPC a character kills while under the ritual effect (it wards off Arkay and Tribunal temporarily). To take a corpse, you must 'dispose' of it while under the ritual.
Guards will react to carrying corpses or having undead follow the character. They react, violently. Town people don't react yet, I need to fix that dialog.

Advanced alchemy preps aren't available, yet