Necromancer is... well.... a necromancer he turns dead people into zombies, these zombies will follow all order from Necromancer (only dead people though, that why he might kill some people to turn into zombies)
Necromancer wants to turn Alchemist into his zombie because Alchemist can make potions, if necromancer turns alchemist into a zombie then Alchemist can teach the zombies how to make potions (also Necromancer lives right next door to Alchemist)
Necromancer DESPISES Guardian Angel 