Need some advice on security deposit

[Gregory Massi]

Hello biggerpockets...the lease on the my condo is coming to an end on July 31, 2018..i was just recently at the condo with my real estate agent and photographer (to get it ready to list) and notice this black soot throughout the condo (on the walls, ceiling, kitchen cabinets, trim, windows, etc). i asked my tenant about this and he said it was caused by the air conditioner (central air) in december...he said they were doing work on the roof and something they did up there caused this black soot to spread throughout the condo...the condo needs to be completely repainted...i was just at the condo today and tried to clean some of it up but its not coming off...

i do not believe my tenant for the following reasons:

1. why would they wait 6 months to tell me 

2. why is the soot randomly throughout the rooms and not concentrated by the vents

3. I removed the vents and reached into the duct and there was no black soot.

4. also i smelled weed in one of the bathrooms but i am not sure if weed or any drugs could create a mess like that.

I think they are not telling me something bc they dont want to pay to repaint the interior...what can i do about this? how can i take there security deposit?

Any information or advice would be helpful (and yes i took photos of the walls and ceiling and vents)

Thanks,

Greg