Ric and Otherhand, thank you so much for adding so much significant information. There is a lot to process there.
'Mercy killing' could not have been a RATIONAL decision. No one in their right mind would have done it in that visibly close to civilization. The remaining possibilities: heat-crazed despair, drug-crazed delirium, or a planned murder (albeit perhaps an insane one, per Ed's very valid point that schizophrenia manifests at this age)?
I would not rule out 'heat-crazed despair'. Even though it seems so intuitively unlikely lost people would turn away from an easy downhill route and go back uphill, or commit suicide with buildings visible below, I do think it's possible. They may have seen the buildings, and then turned back up the hill with a vague idea of climbing a little higher to gain cell coverage--then, when they couldn't get it, turned into the small slice of shade offered by the side canyon to rest. At that point, perhaps, Nguyen was in severe physical distress, perhaps screaming for Orbeso to do something. Remember that one of the primary symptoms of heat exhaustion is loss of judgement and ability to think clearly. I'm remembering the guy who died on Skyline of heat exhaustion who was found sitting bolt upright not two hundred yards from buildings, with a half-full bottle of water. Clearly, his brain had stopped being able to function at all, even at a primitive level. As inexperienced hikers (none of their social media showed any pix of them hiking,except for one of Nguyen with friends at potato-chip Rock), they may not have understood that civilization was relatively close or that their bodies actually could have gone further. We've all had bonk moments (well, I have

) where I despaired and truly thought I could not go on another step, even though my rational mind knew I was only a quarter mile from my destination. Multiply that despair with dehydration and/or drug-fuzzed brains and, unfortunately, a gun close to hand ...
Or, no--and it was flat-out homicide. For me, the key would be retracing the path they took to the final location and determining how long it took them to get there. Assuming they did come down the main north-south wash from the North View trail, I wonder how long that total trip might have been from car to FL? Anyone care to hazard a guess?
If it was under a few hours, what happened was not a mercy killing, but either a planned murder, or a drug-trip-induced murder.(remember, sheriffs DID find 4 different hallucinogens at the AirBnB, their social media was full of drug refs, and taking shrooms at JTNP is such a 'thing' its called The Joshua Tree.) But, if the tracks suggest it was seven to eight hours and a highly erratic route, then what happened was not a planned murder.
Ric's map shows a point at which blood was found, and footsteps in very disparate locations, which seem to suggest a convoluted or confused route as well as an injury. The blood, the terrible heat of the day, the scattered footsteps, the drugs at the AirBnB, and that the hike had been planned by Nguyen, not Orbeso--at this point, I'm leaning toward the lost hikers in (irrational) despair thesis, with the probable factor of drug use (even if it had only been the night before) causing some of their confusion. I do think many of the hikers on this board are so highly-conditioned that it might be hard for them to picture how hard this hike would be for 'normal' people. I'm not highly conditioned, so I can easily feel how this hike could rapidly devolve into a life-threatening situation.
I agree that photos on their phone would be a key indicator of what was happening. Another phone question I have is about the pings--not their accuracy, but whether these were attempted phone calls, or merely the 'handshakes' of passing coverage? Would their phone chips records show whether or not they'd attempted to call for help? My phone has a directory that shows a record of my calls, attempted or otherwise. This too would be key in determining what happened that tragic day. A lack of attempted 911 calls would make it clear they were not lost.
Q: How many therapists does it take to screw in a light bulb? A: Only one, but the light bulb has to want to change ...