Random thoughts:
The wooden dowel drives me nuts. If it had a blood smear/bloody hand print on it, then it seems MC was injured before he picked up the dowel. There was a long gun kept in the shop ( hanging on a wall, or above a door, or something like that), but if he was attacked, he obviously didn't have time to reach the gun. Did he grab the dowel as the nearest item to try to fend someone off? If so, why was the dowel found leaning up against a vehicle inside the shop ? ( per VI) If he became injured another way and was by himself, why did he pick up the dowel?
The driver's license: If MC removed his DL from his wallet himself, did he do so before he was injured- because VI reported there was no blood on the wallet( no blood anywhere except a smear on the dowel and the drops on the floor). Then there's the age-old problem of why? Why would he have taken just that, or why would an attacker? In researching, it doesn't seem like it's all that easy these days to use someone else's DL, but real documents like those are probably still stolen and sold to bad guys, and used in one way or another by those up to no good. Early on in the case, when I was leaning towards a walk-off, I was told that all Texas residents need to cross into Mexico was their DL. I don't think this is the case these days, but I'm not 100% sure.
We've talked a lot about both these things, but they've been swirling around my head a great deal lately and I keep trying to connect dots. I do have more thoughts about these things, but am looking at every possible angle I can come up with. Nothing makes sense to me and nothing fits entirely. Not murder, self-harm, or intentional walk-off.
If MC picked up the dowel to try to fend someone off, I'd lean toward that someone having a knife or something else sharp, and not a firearm. On the other hand, that dowel could have nothing to do with anything and was just something MC picked up and moved, for no particular reason. I don't believe that, but it's possible.