(via splinter:dots)I started playing today and made it to Arnika, so I am gonna reply now before I forget... This is not a spoiler, but mainly what happened to me...
I headed the same way u guys mention...I reached the teleporter and made Myles (the rogue that greets you upon entering Arnika) pick the lock. He had 37% lock picking...and like 8 tumblers to handle...after trying for long I had to use knock picker and found after 3 tries with the spell I could hold more than 3 tumblers at once (4). I tried for around 5 mins to lift the rest and finally did it. Not much thrill...since there is nothing on the other side...However, I came up and talked to the clerk, the bank employee, I tried to find more info on the door I just picked, to provoke a reaction. Nothing. I leave the conversation and she suddendly became hostile...summoning guards. I had to bash them all to death including the woman...whom gently handed 2500 gp upon dying...shame I canīt make deposits in that bank anymore... bah...the vaults werenīt safe any ways 
This had no influence on my relationship with police officers patroling the city. I have yet to check with Traiman in the HQ to see what happens.
Damn combat...monsters popping outta nowhere are ANNOYING...and my inventory is filled with unique items I cant find a proper use... 
Hope this helped.
After replaying this segement of the game several times I was able to repeatly rob the bank.By using the "sonic boom" spell cast near Lorac to initiate combat, she becomes "afraid" and summons the bank guards. During combat I was able to prevent my players from attacking her and she ran out of the bank. When all the bank guards were dead combat finished. Then I hid in the elevator and rested. When I came out of my hidding place there was Lorac back at her spot behind the counter. I re initiate combat with the "sonic boom" spell and begin all over again. I made sure that my players did not attack Lorac to the point of having my priest cast heal wounds on her if she received any damage. When she becomes afraid she runs out of the bank. After beating the bank guards combat ends.
I was able to repeat this cycle at least 6 times before Lorack persisted in attacking my party even though she was afraid. This netted me a great deal of gold and goodies that I was able to sell off for more gold.
Have a nice day.
MM