I wondered that too. Why DIDN'T he take the bottles with him in the first place. It's because yes, he did want it to look like an OD.
But then he didn't expect to run into Moe and company in the lobby. At that point he was forced to go back up to the room with them, and had to change his plan. Because now everyone was there and they could attest that Anna was fine when they were there or she was sleeping. No sign that she was ODing.
So now he had to get rid of the drugs because they had his name on them. I wonder if he wore gloves when he opened the bottle so as to not leave his own fingerprints on them. And maybe he made her touch the bottles to put her fingerprints on them.
I'm sorry to keep asking the same question, but this is really bothering me. WHY didn't he expect to run into them? What went wrong? He did expect them to come back SOME time, didn't he?