Yeah, you do need to put the body together fully in order to progress further. Otherwise you will just loop infinitely. The head is in a small bedside table that you find in the first subway car, the one where the body is in.
Hey, yesterday I was playing it and tried to open that bedside table, it sounded like it unlocked, the camera zoomed out but the lockpick stayed on and I wasn’t able to open it in any way. Hope you can fix this bug soon, thanks for your quick responses and this great game!
The lockpick "bug" is only rarely happening, I'm not quite sure yet why, but I am working on fixing that as soon as possible. Sorry for the inconvenience.