After you turn in the herbs for Do You Believe? talk to Ishaq to flag this one - you need to head to the marker and examine the blood fountain - then follow the tracks from it to the hotel.
In the hotel you will need to force open the lift and climb up, then make your way to Room 206 - which is locked. Head back down and you will find the Staff Area keycard on the stairs - use that card to get into the Staff Area - kill the infected there - and then take the Keycard for Room 206.
Now retrace your path to Room 206 and use the keycard to gain entrance - inside you find evidence that Rais has been here - and when you pick open the crate you find his gun. Loot the rest of the room and the quest is completed!