Just keep going through the whole thing, when you're done, the tour guide will say that the tour is over and you can exit out that way.
go down to the exit of the underground tour and meet the person who knows that the scream will be stolen
go to the underground tour
The shady guy meets you at the Docks exit from the Underground Tour, and tells you to enter the museum to stop the theft.
you have to take the underground tour
go in the underground tour
at the docks
A green beret is worn by the Tour Guide on the Underground Tour on Counterfeit Island.
You have to get a job at the museum after you take the underground tour
It is at the bottom right of the Docks scene, right of the Underground exit.
The "shady guy" (strange man with the scar) is at the exit of the Underground Tour. He suggests you return to the museum and get the job so you can stop the theft of The Scream.
It is between the Underground Tour and the Police Station in Downtown.
In the bin near the tunnel entrance.