@Yi Zhao
I would’ve knocked on the door and given them a vaporizer for their ganja so at least they can make the smoke odorless lol and after they praise what a wonderful landlord you are (with red eyes) tell them they can either Vape their weed in their apt. with that or walk outside if they need to smoke “flower” but they can’t do what they are currently doing. If they cooperate even a month without a complaint, send them a quick thank you card and gift card telling them you appreciate them working with you!
Police reports for that in MD will help build a case of complaints from the one tenant but I don’t know how far that would go in court only because the person could have a legal license to smoke it in their residence. The grounds that may help is if you can argue that it is negatively affecting the health of your other residents and making for an unsafe living environment (especially if any children or infants are around).
I think it’s always best to find a creative middle ground and if they don’t play than lawyer up and then get aggressive quick.
Best of luck!