Agreed with those saying this person is not a reported MP anywhere (unless he's the real Bobby Dunbar, which I'd strongly doubt). Ruess is definitely a good guess jmo, but the timing doesn't seem to fully line up. Would wonder if it was Gerald Clifford Bartlett if the pants were government issue, but it appears they weren't. Still, you kind of wonder, there's only an image of Gerald from when he was 12yo, and he'd be maybe 27 in 1931, 4yrs off from an initial estimate they gave for this decedent.
I know the reports are saying the pistol's cheap, and the clothes are cheap, but it's the Depression and the person's in the Grand Canyon. Up until the time he did himself in, it sounds like he was doing pretty well for himself, all things considered, even if he hitchhiked there, which was common in the era. A lot of people at this point are in Hoovervilles in rags. So why did this person end up in GC and do this? My guess (?) is that he had become recently unemployed.
Seeing that this person they found was really, really muscular, really defined "robust" muscles (think this is from the
Unsolved Mysteries episode). So there isn't any fitness craze in this era, that's sort of unusual (arguably) for someone even 18yo in this timeframe, I would think. So...maybe an athlete, a very good one, maybe minor league baseball player recently let go, the minor leagues were devastated by the GD; seeing the Miami (AZ) Miners seem to have become defunct in 1930. The Mesa Jewels folded in 1929. OR maybe ranch hand/cowboy? We may not have all the clothing (Where's the jacket?), but it sounds like what he was wearing couldn't be excluded as clothing worn by a ranch hand, although I mean, no cowboy boots. Ranchers were hit especially hard in this era. ORcircus worker? Circuses were folding right, left and center in this timeframe. If he'd worked a circus, he might be in a role where he needed a lot of agility/strength. And with a circus, he likely had ridden plenty of trains and knew the lines that go into GC. There's the notorious "redlighting" of circus workers, where they'd be left behind at the station so the company didn't have to pay them. And evidently, there are "Showmen's Rest" burial areas in many cemeteries, these were blocks of plots for deceased circus workers, and a lot of the plots are unmarked or use nicknames because of the transient nature of the business.
His circumstances may be something of a mix between transient and local, someone not originally from AZ that ended up there and stayed there, maybe even prior to the GD. Shoshone Point is not that widely known, it's not marked, and it's pretty secluded. Also, where's his jacket? Unless he's out mid-day summer, he can't really be going too far without one. Even for a hike that might go into later in the day, he'd want a jacket. Suspecting this person knew GC. Maybe he was in a juvenile home not all that far away, there was a Mother Higgins School out in Tucson and a State Industrial School out in Fort Grant. Maybe he was originally from a wealthier family that lost everything in the GD, might himself be the son of a suicide. Also both Tuba City Indian Boarding School and Truxton Canyon Indian School would only be about two hours away, based on what I'm reading. What about someone from the "Little Mexico" community that formed on the South Rim during the 1920s and continued into the 1930s? They built a lot of the park's infrastructure. That area where Little Mexico was is a stone's throw from where the Doe was found. (People in Little Mexico would probably also have been concerned about GD "repatriation drives" where people were being deported back to Mexico.) He doesn't look in the sketch like he's Latino or Hispanic, but jmo, those sketches can be off. He looks more possibly central or eastern European jmo, & so also wondering if he emigrated to the US and had no family in US to report him.
BUT with all of this said, in 1931, the tourism to GC remained substantial. And that means this could be literally anyone. All we know about him, assuming he's not a reported MP, is that he's not a reported MP. And we know his clothing, height, age, gender, and this point on the muscles, probably his hair color, and little else. It's not much to go on, glad the case is with Ramapo.
Question. I'm seeing guns are prohibited in the GC unless he acquired special permission in this timeframe (who knows on practical enforcement of this then, though). Provided he didn't want to risk having the gun confiscated, where exactly did he have this firearm concealed? Did he just tuck it into his waistband? Did he know how to access the park to avoid a check point? Even if he did, I mean he wasn't walking around, I'm sure, with the weapon in his hand. What a truly bizarre case.
www.ramapo.edu
www.newspapers.com
My new, completely silly theory is that the real Bobby Dunbar is actually the BCJD. Sure, sure, the time frame doesn’t add up at all, but who can say, really? 
