Bought Foreclosure at courthouse.

[Will C.]

Hello all! Long time browser here, but first time poster.
I've been doing real estate for years out in OC California but am now in the DFW area in Texas.
I bought my first "courthouse steps" foreclosure the other day. I'm unclear on a couple of points.
I cannot determine the occupancy. There's a run down truck in the driveway that hasn't moved since I bought the house. There's a dog in the house. There are never any lights on day or night. No answers at the door. Repeated attempts with notes on the door and letters in the mail. Unanswered phone calls. The notes eventually get taken down along with all the ads that get distributed in the neighborhood. It very well could be a neighbor or friends getting mail and feeding dog, but I'm not sure.
So I'm just assuming that the previous owner is still there, but what if this continues for several more days. At some point do I assume that it's been abandoned? I mailed the "notice to vacate" the other day. Do I see a whole eviction through, or am I supposed to break in and re-key? Do I mail a 5 day re-key notice? And what do I do with his stuff, dog, and truck?
I guess another way to ask the question is if from the beginning I looked in the house and didn't see anything and it looked completely abandoned, what would be the legal method of gaining control of the house in that scenerio?
Thank you in advance for any help that you might be able to give!