A Scary Thought on the U.S. Justice System

Most, agree that the U.S.  justice system is the best in the world, yet, note the following:
Suspects have been brought to trial — and convicted — in cases where not only is the body missing, but physical evidence linking the suspect to the crime doesn't exist

• NO BODY
• NO PHYSICAL EVIDENCE

If there is no body, how does one prove any death has occurred? much less a death resulting from so called "foul play"
If there is NO EVIDENCE linking the suspect to a crime, that in itself, also cant be proven to have even occurred, then just how does someone vote for conviction?
THAT IS a scary thought indeed. It makes no logical sense, at least to me, and represents an excellent reason against the death penalty. Not that the death penalty would be sought in such a case, i doubt it would, but still, it does show how someone could receive the death penalty on less than solid evidence.
Now i readily admit that if it were a loved one of mine missing, i too would want SOMEONE, CONVICTED of SOMETHING. I also admit this is a foolish stance, a selfish stance, one taken out of my misery rather than out of seeking " justice"