Why do you wish to get involved in something that should be sorted by management?

this would be dependent on your unique sense of morality, not a question others could answer I would think. I would only do so if I thought it would create a useful outcome for myself. Otherwise I don't care what other people do for lunch so long as my own time is accounted for properly.

@BryanH, he means this guy takes a 30 minute unpaid lunch, but is only working 8 hour days, so with that 30 minute lunch he's actually only working 7.5 hours, but is stating he's working 8 hours, just not taking the lunch out of his work time.

Updated your question - please verify I got it right.

Unless what this person is doing adversely effecting your workload at work, you do not have to to anything morally or otherwise. If you are noticing this behavior, I am sure some others too. If I were you, I'd let someone else to be the bad guy. You know someone will say something about it. Probably the office gossip person will not keep his/her mouth shut. Why be on the cross-hairs yourself. If you do it to someone today, someone else or probably the same person will watch you to see you falter and report you.

Are paid per hour or are you on salary?

Are you the only one of your team that noticed this problem?

Does the co-worker who is leaving early clock in/out, sign in/out or swipe their access card when they arrive and leave work? If so, then management already knows (or should know) about when he comes and goes. Also, perhaps he has special arrangement for this. Are you sure he doesn't arrive early, or that he doesn't return to finish his workday after you have left for the day?

are you making a question for 30min gosh

Not to be snarky, but if you are spending company time monitoring the coming and going of co-workers, you're not really putting in your 8 hours either :)

re: 'morally wrong' - you're not the moral police.Just take care of your own side of the street. Really, more problems and unhappiness are caused by people upset that others aren't behaving the way someone else thinks they should.

is this a salaried role

@MichaelJ. Perhaps the asker leaves a little late to compensate for the time spent people-watching.

What is your title/role with this company? Are you the person left in charge when your manager isn't there? If not, let your boss worry about who is working and who is not. If your manager cares, she'll find a way to know. If she doesn't care, then you shouldn't either. Jumping on a moral high horse often has a way of backfiring.

I was in the same situation as your co-worker. I always left early when the boss was out. The reason is that there was no chance to leave in time when the boss was in-house. He always wanted to discuss the next work tasks in late afternoon. Leaving early when he wasn't around, didn't make up for the overtime.

@Change: What would you do if you had to go pick up your kid from some place 30 mins before your work time was over? And what would you want other people to do in that case?

@Mehrdad what would you do if you have to pick up your kids 4 hours before your work time will be over ?