Guild Wars 2

I saw a thief in the PvP hall. He wore a sneakthief armor and was equipted with two pistols. BUT. Around his right arm there were three blue glowing and flying daggers. It looked so coool. What is it?

Retrive turret parts stolen from Kinar Fort:

I have already 16 turret parts in my inventory but I can not give them to Sentinel Darktounge. When I click to the “I’m helping. Here’s what I’ve gathered.”, Darktounge is talking, but my contribution level remains zero and the turret parts stay in my inventory.