I've jsut got out of the vault after photographing the Rinaldi objects that are in there, and Anna has made off with the final bone. Marshall suggests to use the bone traser to find her, but I'm confused on how too. I though I needed to follow the higlighted arrows like the directional arrows in the casino level, but that doesn't appear to work, because Anna gets away and I fail the mission.

I would be grateful for any suggestions.

I'm such an idiot!!!!! I worked out where I was going wrong. I was going up all the ladders into the museum, when I should have only gone up the 1 ladder after the cutscene where Anna blows open the fire door, and turned left to the fire door.

Oh well never mind, I got there in the end!!!