Experienced investigators know that getting to the bottom of a mystery requires uncovering the Who, What, When, Where and Why of the crime. In Mystery Express, these elements are revealed in the 5 Crime decks: Suspects, Modus Operandi, Time, Location and Motive.
There are two identical copies of each Crime card (except Time cards which have three). Since 1 card from each category is hidden at the beginning of the game, to rule out a specific crime element you must see both of the identical cards - or all three in the case of the Time cards.
For example... Once you are sure you have seen both copies of Dr. Rajiv's Suspect card, you know he cannot be the murderer.
However, don't jump to hasty conclusions - unless you see both on the same turn it's possible you may have seen the same exact card twice and the good doctor should still be under investigation!
To get a jump start on your investigation, at the start of the game all the remaining Crime cards (except Time cards), are shuffled together and you are dealt 7 of them. If you are lucky enough to get two identical cards, you can already rule out that Crime element. Based on this hand, you know that the murder did not take place in the Smoking Car.
Deducing the time of the murder may be your most difficult task. There are 8 different possible "clocks" to choose from and 3 cards for each time. Not only that, but you are only allowed to see the Time cards when visiting the cities of Strasbourg, Wien (Vienna), and Budapest - and even then, only for a few short moments.
You'll have plenty of other chances to view additional cards throughout the game. You'll get a chance to peek into other players hands, draw more cards to your own, chat with the Conductor, and use your own special powers to get more investigative clues...