Vanished (help me outline a short film about a bank robber's impossible escape)

Got the idea to do this story about a male bank robber who is chased by a female cop (she's the protagonist). The chase is short and ends when the robber runs into a public restroom. When she runs in after him, he's gone. No windows, or if there are then they have bars on them. He's gone. Gone enough so that when police investigate further (checking for trap doors, checking outside, ripping up the floors, etc) they find nothing.

I already know how he vanishes. But I got a couple different ideas for directions to go, and need some help deciding what to do.

• I want this to have more action than just the chase scene. I don't want it to be all Mystery for the rest.

• But I do want to leave loose ends to tie up at the end. I want questions to be left unanswered til the last few minutes. That kind of ending.

• It's supposed to be thirty minutes, thirty pages. Three acts, not five.

The cop could find the robber in the 2nd act (after police have probably spent two whole days investigating the bathroom), leading to...

• Us finding out that she's there to get him free, and that she's been in on it and getting a cut... (little to no more action, either they both get away with it or just one does)

• OR she and another cop go back to find him, he shoots the other cop, and forces her to help him out. (more action, but a dead end. how does she help? how do they cover up the dead partner? what happens in the end?)

Anyone wanna give me a hand? What would you want to happen? What would shock you best?