Although the culprit's face is revealed, it just doesn't seem to fit. What if, he has an accomplice to take care of 'outside' matters?
The culprit and the fake doctor are probably two different people. The fake doctor has a smooth face while the culprit has a rough face. During the hospital kidnapping scene, the culprit must've already started the car and waited for the victim. There's no other explanation as to how quickly they escaped. It would've taken more time if the fake doctor had to put the victim in the car, then move to the front seat and start the car and drive away.
Sit back folks, for this might be long.
The Possible Accomplice of Culprit:
Take a note of his face complexion, not-so-full pink lips, dark hair and shoulders.
A full-length pic:
Take note of his shoes and how his right hand appears pinkish/reddish.
The culprit disguised as the doctor: Take note of his spectacles, dark hair and thin eyebrows.
Picture with hand:
Right hand appears reddish/pinkish.
Another full-length pic: Take note of his shoes, which are different from the ones he wears after, showing that has more than one pair of shoes and that's why the footprints were different in both cases, or, they really are different people (who are accomplices).
For reference, the real doctor:
The culprit did a pretty good job of disguising as him, except, their lips look different.
And now, here's a picture of Hyuk's elder brother whom he 'trusts':
Light complexion, not-so-full pink lips, dark hair, pinkish right hand and similar shoulders to that of the 'accomplice'. And if you look close enough, you'll notice that he has thin eyebrows too.
Coincidence? I think not.