I'm trying to complete the "Auriel's Bow" quest for Therana & supposedly its possible to pickpocket the npc that has it. Now here are my adjusted stats after casting a bunch of spells to increase success:

Agility 200

Luck 200

Sneak 160

Chameleon 100%

Invisibility 100% (Cast after chameleon)

Still catches me every time despite being behind him & partially behind pillar. I can not kill him as I am the leader of the temple & if he dies I get expelled. Any suggestions?

P.S. I tried taunting him thinking I might be able to kill him without penalty if he attacked me first & that also didn't work. On a funny note, the first time I tried doing it he aoe'd one of the other npcs & killed them & I was blamed for his crime lol odd....

Thanks for your time

Are you using the Code Patch?
Because pickpocketing was pretty broken in vanilla, but the Patch has a fix:

It's still probably going to be difficult though.

And make sure you have full Fatigue.

Yeah, sneak is bugged in vanilla Morrowind. It doesn't properly take your skills into account. Try it with the patch, as Pluto suggested.