The circumstances surrounding the location and storage of the gun bring serious question to the nature of the firearm. I can think of no legitimate reason for the gun to be stored there.
First, the gun is of relatively low 'street' value and hence common type and caliber among thugs (or at least that's my opinion). One also found in low income areas, probably owned by a small statured person that owns 1 or few handguns (kept it in the case, under his/her bed or in her closet). A novice owned it because there are two loaded magazines, but the gun was empty.
Probably about $100 on the street. Found unloaded with 2 full magazines, all in the case.
The most likely answer is that someones' home was burgled and this gun was the 'loot' found under some unlucky person's bed, or in her/his closet, etc. The thief put the gun here until he could find a buyer because he doesn't want to get caught with a gun, and a hot one at that. And your friend found it.
Maybe the victim was unharmed, or maybe strangled. We don't know. Maybe the victim came home and reported the gun stolen. Maybe she has insurance or maybe not. Maybe the gun will be replaced, or the person can't afford to replace it.
But the handgun has nearly no value, maybe a couple hundred bucks tops.
The greedy thing to do would be to keep the weapon without running any checks. Bad karma.
The semi-ethical thing is to run the checks through NICS using a FFL to see if it's hot. If it's not hot, keep it.
The ethical thing is to contact the police and explain the situation and get them to agree to turn it over to your friend if after a reasonable waiting period nobody claims it.
The friend may also inquire as to whether there have been any breakins in the area - although that may be a wild goose chase in some neighborhoods.
Also, keep in mind there is someone that probably stole it and may come looking for it and your friend may be a likely target because he works there as the maintenance guy.