"nate only killed those old people because the guy was shooting at him first for no reason!"

ok but

the game heavily implies that nate had been at the pit stop at some point before he came across russell

  • when nate is trying to convince you to run over to the truck after the first few shots are fired, if you choose, “i’m gonna get shot!”, nate replies: “no you won’t! this guy can’t hit the broad side of a barn!” he seems to know the skill of the sniper (or even the fact that the sniper is an old man), despite only coming across him less than a minute prior.
  • he seems to know his way around the gas station pretty well, even though he claims he and russ had never been there before and were just “passing through like anyone else.” he knows exactly where to go to take cover from walt’s bullets, and starts almost instinctively walking to the back lot of the diner before russell can even dust himself off. the whole thing just seems very routine, like nate had gone through it before. 
  • the most important tip-off is when russell asks nate what walt is talking about when he accuses nate of attacking them once before. russell says, “a mask? what’s this guy talking about?” nate replies, “fuck if i know, he’s crazy.” russell isn’t convinced, and asks in a very accusatory tone, “have you been here before?” nate doesn’t deny it. he doesn’t say, “no” or “hell no, man!” or anything of that sort. he says, “russell, don’t you start.” 
  • i guess my question is: why would telltale even have russell ask nate if he had been there before if they didn’t want to imply that nate had? why would they have nate reply with dodgy answers if they didn’t want to insinuate that he had something to hide?

we don’t know much about nate’s past or what he had been up to before he came across russell, but i think it’s safe to say that, given the game’s implications, he had come across walt and his wife at least once before the confrontation in russell’s story. then, once he picked up russ, had gone back to do exactly what walt had accused him of: finish them off and take all their stuff.