[Nancy1999]

I agree with the above posts, but there is probably a leak around the window. Sometimes just adding caulking can help. Definitely call the complex manager; this is the sort of problem that they need to be aware of. Killing the mold, won't keep it from returning, and it the meantime it could start growing in the insulation between the walls.

You posted just ahead of me, your bathroom doesn't have adequate ventilation. Call the manager, you could be held liable for not informing them of this problem.