When Max meets up with Lucas inside the Fine Arts Building during Chapter 2 of Life is Strange: Double Exposure, she'll need to look inside his suitcase to find out what he's hiding in there. But Lucas won't just offer up his briefcase; instead, you'll need to distract him and have him look away. Here's how to open up Lucas' briefcase and take a look inside.
Finding Lucas' Briefcase
After meeting up with Lucas at the café at the Fine Arts Building, wait until your conversation ends and Lucas gets up from where he's sitting. He'll lock his briefcase and get on a phone call - so now is your cue to act. Change to the Dead timeline using the gateway nearby, so you can make your next move.
How To Distract Lucas
In this timeline, interact with Lucas yet again and have another conversation with him. Listen to what he says and wait until the end, so you can try to distract him.
To distract Lucas, you'll need to make some... "adjustments" to his standee. So, go to the cafe counter and pick up a marker. If you're having trouble finding it, look at the right edge of the counter. You can "Examine" it if you'd like, and then select "Take."
Now that you've got a marker in hand, you can head over to Lucas' standee and vandalize it using your marker.
You'll have two choices for how to vandalize the standee, but these are just for fun - pick whichever one you'd like. Regardless of which form of vandalization you chose, you can now head over to Lucas and let him know what happened... without letting him know it was you, of course!
With Lucas distracted by the standee you vandalized, take this chance to grab the key to the briefcase. If you'd like, you can also take a picture of Lucas as he's looking at the standee and post it to Crosstalk - though this is entirely optional.
How To Open Lucas' Briefcase
Now that you've got the key, it's time to swap back over to the Living timeline and open up Lucas' briefcase while you've got the chance. He's still talking on the phone, so you won't need to do anything to distract him this time. Use this opportunity to open up the briefcase, giving you some insight on what's inside.
With that, you've distracted Lucas and opened his briefcase, tipping you off to Lucas' secrets. With the knowledge you've gained from what's inside, Max can move on with her adventure.