None of the above is really wrong. Nearly all are quite valid comments, but then each of you has a lot more travel experience than this young couple.
It is a given that the couple made a serious mistake in bringing, and then wearing valuable jewelry on vacation, but the resort seemed so remote, and so safe that they were not alert to any possible danger. Everything about the resort gave them a feeling of security and safety, and being inexperienced at such travel these folks were simply not aware of the risks of strolling on the seemingly empty and isolated beech.
Yes, there were guards, but the laid back, relaxed attitude of those guards, and their seeming lack of concern was very disarming.
This is a "remote", "Exclusive" resort that they were flown to by helicopter, and it's very remoteness lent it an air of protection from the big bad world. The long, isolated, beautiful and romantic looking sandy beach that the resort sits on invites exploration, and at no time was there ever any suggestion that they should not walk it, or even that they should be cautious. Other guests were making the same strolls, seemingly unmolested, so the couple was just not as careful as they now realize they should have been.
This sense of isolation appears now to be just an illusion, because they have checked, and a Google Satellite image shows that sections of seemingly remote beach they were on are bordered by a road that was not visible from the beach but which comes within possibly 50 yards of that beach in spots, where it is thought that the attacker was waiting for them. It is suspected quite strongly that this man had been prepared, and then alerted by guard(s) when the couple left the resort for their stroll, but of course this is only speculation at this point.
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The entire point of my post was to pass on a word of caution to other travelers that even seemingly remote and safe destinations may hold more risk than they appear on the surface, and for travelers to be careful about both their surroundings, and what valuables they bring and wear on vacation.
What seems so obvious to experienced travelers, like so many who have posted in this thread, is not always so obvious to novice travelers, visiting foreign destinations for the first time.
It is the novice or relatively new traveler, who may be preparing for the first exotic vacation of their lifetime, and researching resorts and travel destinations that I am trying to alert about some of the risks they will not read about in the travel or resort brochures, or on their web sites. Such a traveler may not be even remotely aware of State Dept, or travel web sites that provide travel safety information, or alerts.
Being assaulted, and robbed with a weapon while strolling hand in hand on the sandy beach by an exclusive high end resort like Sivory Punta Cana, is NOT something you anticipate while reviewing their advertisements.
These people have been sharing their experience, and lessons learned, to help better prepare others as inexperienced at world travel as they were.