Wondering if Swimsuit Boy was in town for the Eagles at Sam Houston Coliseum in June (or July, date disputed) 1972, they were opening for Jethro Tull. Swimsuit Boy's outfit is screaming Texas to me, but he doesn't appear to be from TX as an MP, jmo. If he's not from TX, he was maybe going to see a very Texas band like the Eagles, and in Texas.
As I was looking, I came across Donald Curtiss, missing from Tucson AZ November 1969, graduate of Chicago area high school and son of a business executive there, he was looking for gold in the Catalina Mountains, his friend left him once they entered into a very remote area and Donald had an asthma attack, the friend was going to look for help, and searchers came back scouring the area for Donald, never found him. Struck by the resemblance, Donald Curtiss on left, Swimsuit Boy on right:

Other pics Donald Curtiss:
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18yo in Nov 1969, 5'6"-5'8" Donald and the other young man he was hiking with met at the Tucson YMCA, evidently Donald had been having troubles with asthma and had gone down there to earn money for college. Tucscon would definitely be a good climate in terms of asthma, and Houston TX would not. He had an inhaler on him and a metal detector. Metal detectors are generally pretty sizey, I would think especially in that timeframe. Did they ever find it, I wonder?
And this article on Namus says the friend had noted Donald had an asthma attack and had severe leg cramps, he couldn't walk. Swimsuit Boy had that mild spina bifida which might have affected his walking. Now, I am seeing, though, that certain asthma medications can cause severe leg cramps, although the answer on whether the person would actually be unable to walk is much more "iffy." Swimsuit Boy also had good dentals, and it appears from the image of Donald smiling that his were probably good.
The YMCA note also makes me a little nervous because Houston did have a dorm YMCA at this time, from what I read. Whether a Heights branch existed with dorms, I've got no idea. Just looked it up and there is a Heights branch, from what I can see. Uncertain as to whether it had dormitories for overnight. Really wondering on that because of strong resemblance, jmo. Strong resemblance notwithstanding, though, the circumstances don't seem to lend themselves to the idea at all, and LE doesn't suspect foul play,for Donald from what I see on another source. I still can't get past that uncanny likeness, though, between those first two images, the one of Donald and the new likeness they produced for Swimsuit Boy. And also kind of curious about how the friend noted seeing .22 caliber cartridges in an area where he and Donald had been at one point. I wonder what that was about.