This guy did this on purpose - but lots of parents don't. It can happen and does happen, like any accident, and in my personal opinion, it is not a criminal offense, and should not be prosecuted at all (cases like this asshole excepted). I know for a fact those parents will suffer more than you could possibly imagine.
It came close to happening to me, and I don't think anyone here would or could accuse me of being a neglectful mom. Our regular morning routine was broken up by a doctor's appointment, and I got halfway to work before I realized I had not taken Katie to the babysitter. She was asleep in her car seat in the backseat and I completely forgot she was there. Scared the living shit out of me, because I was only too aware of what could have happened. She was newborn little, I had already gone back to work and was tired from being up all hours of the night nursing, and was driving on auto pilot. So for all of you who say "Oh, it would never happen to me..." - you can't say that. Because yeah, it could. All it takes is a change in routine or a sleepless night or a stressful situation to distract you. You can't tell me that you have never driven to work on auto-pilot, and just kind of snapped back to yourself and realized you were at work and can't remember the drive in, especially if it is a daily routine.
I turned around and took her to the babysitter and all was well. But I still have nightmares about this incident and always will, and nothing even happened.