You could use something like trail cams.

Also I see what looks like a macerator on the sewage line with an electrical connection (to the right of the window).That might be in indication of sewage issues in the line to the street.You might want to have a sewer cam done (by a reputable company).Maybe try to find out the age of the macerator, and any history if issues, and if it truly is a home use macerator vs one for an RV.A home inspection might also be a good move.Also the old cast iron sewer pipe looks to be wrapped with some kind of insulation, you might want to see if you can get any info on pipes freezing in the winter for that building (or if the pipe is cracked and someone tried to bind it back together).Good Luck!

You and the neighbors should consider setting up trail cams or some type of security to catch this guy in action.Mini splits are nice and should be cheaper.

Now you can't discriminate against someone with a criminal background (with the exception of sex offenders) unless you're living on the property like a duplex. 

People are people and it’s just as likely for an ST guest to complain about an LT tenant playing their trombone as it is for the LT tenant to complain about the ST guest having loud sex all night!

[As I learned in Vietnam during the War:  Xin cam on!]

Looks like you're already a Property Manager, so you have that covered, with a little hourly help.It was 100%  all doctors and dentist still not sure what I cam going to do.

I'm thinking of a career change and going to get the CAM license, which has to be held by a broker.

You'd be surprised how evolved it cam become in just a matter of months. 

Don't forget the fact that there are 7 Federally protected classes and disability is one of them (Race, Color, Religion, National Origin, Sex (including gender identity and sexual orientation), Familial Status, and Disability).