If it's the computer he's looking at, sounds like you're right. He's trying to rule it in or out, and I wonder if they've also looked to see if any drugs were ordered online? At first, I was thinking some of the additional evidence Perper mentioned might be something from Daniel's autopsy. Still could be, I suppose.
The only thing that I can see is if there was a search under, say: Drugs, lethal combination and they match his findings. Similar to Scott surfing for for tide data.
That would change it to a homicide investigation and search warrants would be all over the place. I have no doubt that investigators are trying to build a case. Wait and see.
In the meantime: "Hey Howard....yeh, keep looking over your shoulder....It isn't your imagination. Someone is really there.
I think that Howard thought that everyone would absorb themselves into Anna, and he would be just a dude in the background. Well, that didn't work!! Go to Plan B.
Disappear: Go to the house and stay there. You are in control there.....until they kick your sorry a** out on the street.