Just a quick thought about your script. What if at the beginning Marvin walks in front of the car and waves as he goes by on his way up to his apartment? Just being a friendly person.
Stan goes up and knocks on apartment "6." Then the exchange like you have it. Samantha comes out of the restroom. Marvin shows her the cash and Samantha says they forgot to get their briefcase back. They don't have a use for it. They will buy one.Marvin tells her what kind of car they drive.
Stan goes back to Brenda and suggests the both of them should walk across the street to get some chow before they continue. Once they go into the Deli. Samantha comes down, finds the car and lays the briefcase in the back floorboard with a big thank you note taped on it. She goes back up.
Samuel rushes up to his door right behind Samantha. His phone rings. Yeah, he's home and hangs up. Blows Samantha off. She does the six to a nine. Samantha and Marvin sit at the kitchen table next to a window admiring their new windfall.
Brenda and Stan back in the car. He pulls out a black device with a big red button. So long
Marvin and Samuel. He presses the red button and beep beep beep. They both look in the back and each other. OH...Crap.
Back in Marvin and Samantha's apartment, they still count the cash. An explosion and smoke rise in front of their window.
It's just a little spin on your story. Not that your version is bad.
All the best!