This has been my observation in 45 years in real estate investment.  The investors I’ve know through the years who have utilized “sharp tactics”, something less than “honesty”, etc.  ended ended up at retirement with ...

Don't discuss the mold with him because he obviously didn't provide evidence or the opportunity to remedy the situation. 

Unless you have evidence the tenant caused the crack, you are out of luck.It sounds like there should be a bead of caulk between the sink and the wall to prevent water from seeping down.It also sounds like you should inspect at least once a year so problems like this don't go undiscovered for so long.

The tenant having paid full January rent is evidence they intended to occupy for the month of January. 

Send an email to [email protected] with an example of a new law and evidence that it has not been updated in their online files.

When I check local real estate listing it’s evident that a number of these properties for sales are former airbnbs that were purchased in the last 2 years and clearly are not worth holding onto for the owners.

We already hired a lawyer and he is gathering all the evidence he can.

Perhaps the landlord can direct you to the video as evidence, or talk to a neighbor. 

Please see evidence at the end of this email. 

It will be evident if you go to the city where they want to live: Madison State Street,  Boulder, CO , the Hill.