Mystery Leak with Inherited Tenant

[Rob Braun]

I have a 6-unit B class property with all inherited tenants.  It has now been a year and no big issues, moving right along.  All of a sudden I get a call from a tenant saying there is a major leak.  I go over to check it out (I am a DIY landlord), sure enough it looks like a leak in the corner of a room.  It is the top floor unit, so no plumbing above, and the leak seems to have started in the middle of the wall which is odd.  I have a roofer come inspect, and it happened to be when it was raining after a snow/ice storm was thawing out, and saw no issues whatsoever.  Had a mason inspect, no issues with brick.  Inspection report had no issues in the attic.  Has anyone had experience with this kind of issue?  Could it be self-created?  What are my options, since I will need to get it fixed and probably replace the drywall which will most likely need to be done only after the unit is vacated. Thanks!