So, I have a noir story and my leads, an assassin and an escaped con (the former saved the latter and helped him to hide from police) should do some "job" together which would allow them to leave the city and go to somewhere they'd be safe. What could they rob? Mind they're no petty thieves. They need something big, suitable for gentlemen, and not 100% crazy. It could work if it weren't for the old, cunning inspector, some traitors and the laws of the genre, which clearly say they won't make it to the ship/train/plane.
Here is a spin they can hide in the bushes and rob the owner of a high volume strip club owner who brings the cash home at night , the club owner could be mob connected adding additional dramatic tension
What kind of skills does the convict have? Is he a hacker? Hired muscle? Counterfitter? Cat burglar? Safe cracker? Finding a job they can do together will be easier if you narrow down the abilities the convict has.
I agree with Ellipse, what kind of skills do they have? I'd imagine they would need to get the cash quick, for they would be on the run from the police. I'd think the job would need to be hasty, quick and dirty. Perhaps a classic bank robbery would suffice? How about hitting an armored car? Would they know anyone before who had money? Perhaps a rich, yet corrupt, politician or businessman who has large amounts of cash in their estate or yacht. etc etc.
Keep in mind that "convict" does not describe a person. There are a million and one ways in which someone can be a convict (well really just the one, but the path leading there is quite variable). So what did this guy do to land himself in jail in the first place? Is he a career criminal? Is he actually innocent, but now on the run because he escaped? Did he murder someone, rob someone, rape someone, swindle someone, or throw a cigarette butt on the ground in front of a staunch "no littering" officer? I think that when you decide who your escaped convict was before and is now, you'll find your answer pretty quickly. But yes, in general, they're going to probably want something quick, dirty, and as low-key as possible. Like purse-snatching.
Well the assassin could and most likely would be the muscle doing the "dirty work" while convict would do the brainier work I'm guessing? If that is the case have the Convict had been convicted of conspiracy to commit robbery and got arrested by an undercover officer. Now the assassin and convict are gonna commit the robbery that the convict planned for so long. If you want them to have a VERY interesting plot have them dress up in a costume and rob a costume ball. They could be very gentlemanly all the while being able to pull of a big score to net some big bucks. For more awesomeness have a chase scene where the inspector comes in right after they commit the robbery and are getting ready to head for the train/bus. Have them escape on foot and then you can go from there to how you want it to proceed.