I think it's a mistake to speculate the worst about Orbeso. The authorities are not idiots. If they had evidence against him, there would be a criminal investigation.
There is evidence, however, that these two were good friends out for a hike in unfamiliar terrain and they got horribly lost while being unprepared. Both were young, had dated and separated without killing each other. Nguyen clearly trusted Orbeso enough to remain friends and go hiking with him. Orbeso was a security guard, which seems like a healthy, life-affirming profession to me. Not that all security guards are angels, but if we're going by the evidence, my money is on a young man who respects life and women.
Furthermore,
the JTree spokesman said footprints indicate these two may have been going in circles. And like others have pointed out, there are lots of rocks in Joshua Tree. Hard to check them all, or see shaded spots from the air. Maybe they wandered outside the search area and collapsed from exhaustion. Maybe they fell and hit their heads. Or maybe they became delirious, went to sleep under a random rock and never woke up. Very sad.