we have an incredibly mundane, low-stakes Mystery going on in our little apartment tower

Someone keeps breaking in (the lobby door is locked) just to sit in the stairwell, eat fast food and smoke weed. They order delivery to an address in this building, intercept it at the lobby, eat it and then leave the trash behind. Honestly, I don't think anyone would have noticed or cared if they didn't keep leaving the trash behind

My theory is that it's a young man who lives nearby and is scared of his mom seeing him smoke weed, so he sneaks into other buildings to be sure she won't see him.

he should be more worried about what happens when mom finds out he's been littering when there's public trash cans everywhere!