Problem: Chaotic Neutral Vignette

By inference, a 1st-level evil NPC could be "used" as a method for a party to obtain a knock scroll starting with an evil NPC dialogue (or something like), "It's my loot and I'm not sharing with the likes of you!" that could lead to thievery, bribery, diplomacy, intimidation, or combat with the evil NPC.

 

The magic number for the Open Locks skill to open the end chest in the Chaotic Neutral vignette is +5.

That's the lowest modifier I could open the chest with. The character was NOT a Rogue, but had a +1 DEX mod, 3 ranks, thieves' tools (from the opening store), and the guidance spell. (It was a Cleric using console commands to boost his EXP for testing purposes.) The thieves' tools provided a hidden +2 bonus. Without any such tools, there's a -2 penalty (which the tools remove).

Also, make sure your armor and shields are off! These impose an armor check penalty to your Open Locks skill! (Any armor or shield that gives no armor check penalty is fine to leave on for lockpicking in general.)