So many people are making much of the fact that he doesn't wear a mask… the Unabomber didn't, and was only caught by a tip-off from his brother.
Seoul has millions of young men looking vaguely like Ji Young. Anyone tall and fit wearing a hoodie could be he. The victims (other than the very first one that has probably gone unrecognised so far) are unrelated to him. Many don't survive or have brain damage that prevent a testimony or description. Others are made unconscious so quickly they don't have time to make a mental image (like the doctor). And the fact is that physical descriptions are so inaccurate that often the drawings don't resemble the culprit.
The hood covers the facial features that would make him recognisable by street cameras. Gait analysis, fingerprints and DNA only work for people (normally criminals or suspects) who have had these data previously recorded. Indoor cameras he inactivates while preparing the location for the attack.
You may have a point that he's screwed if one of his victims lives to tell the story, but at this point this is quite a big "if".