Some questions about Dungeon Master Guide 3.0 Edition book.

[anvillarroel]

"An assassin prepares and casts spells just as a wizard does."

A wizard needs a spellbook to prepare a spell regardless of whether he knows the spell or not. Therefore an assassin needs a spellbook to prepare a spell "just as a wizard does".

This changed in 3.5 to give them sorcerer style spells known.

Aha, good point on the Assasing needing spellbook, thanks for the tip.