What can I do with the invoice?
1. If you've asked Harvey about his dead boss, he will have given you an invoice. It's the invoice for the antiques delivered to the conference center. The night before, you and Peterson had to carry them on your own to the hotel room where they were supposed to be delivered.
2. Why not go to the antique shop and ask the shopkeeper about it?
3. A clue! If only you could borrow his phone for a while.
4. Take it, then. He doesn't notice much when he stares into space like that, and you're bringing it back anyway (well, pretend you are).