<human>: I am a security guard, and one of the most important things drilled into our heads is "Don't leave your post until your replacement arrives." 

So to the story, I work overnights (midnight to 10am). In middle of my sleep, around 6:30 pm (I normally sleep from 2pmish-10pmish)  I get a phone call from my coworker, Art. He asks if I can come in 2 hours early so he can pick up his daughter from somewhere. I think about it and decide that I can't do it, because 12hrs (plus an hour and 1/2 drive) was not something I wanted to do on 4-5 hours sleep. I tell him no. 

Fast forward a few hours, I show up at my shift and he is nowhere to be found. The door to the security office is locked. I go around to the back entrance, which is normally unlocked to let managers at the business we guard go through. I am able to get in through it. At this point I am thinking he is in the bathroom, but after 10 minutes, I realize this probably isn't the case.  I ask a few people if they have seen Art and they say they haven't seen anyone at the security desk for a little while. 

I decide to check the cameras. I skim through the camera logs and discover that he left at 11:30. Thirty minutes before I was scheduled to arrive. My first thought is to report him.

But, I notice he left a notebook here. It was opened up to a page where he had some goals outlined that basically amounted to getting his life on the right track. SO that coupled with the fact that him leaving may have had something to do with his daughter, makes me hesitant to turn him in. Leaving one's post is a termination level offense. At the same time, there is a very small chance that our supervisor could find out that he left early without me mentioning it. In that case, i could get in trouble for not saying anything.

Can you condense the text into three sentences or less?
<bot>: Should I report a coworker (and possible cause him to lose his job) or should I be silent on the issue and hope the supervisor doesn't find out other ways?