The Marowski Heist

The Marowski Heist is a side quest in Fallout 4.

Detailed walkthrough
In order to obtain this quest, the Sole Survivor must have made certain decisions during Diamond City Blues. One method of obtaining this quest is if Paul died during the fight or if he was brought along with Cooke to the encounter with Trish. The other confirmed method is to choose to completely stay out of the entire plot by refusing to help Paul at the start. If Paul survives the previous quest but is killed later (i.e. killing him at the request of Malcom Latimer), this quest will not appear.

The Sole Survivor will be approached by Darcy Pembroke a few days later, who is investigating the disappearance of Paul. When she asks the Sole Survivor about it, they must tell her that they will help with the investigation or inform her of Paul's death without implicating themselves (if he was in the heist). Then, after a while (about a week) speak to Darcy again to obtain the photo and start this quest.

Due to the complicated nature of triggering this quest, it's easy to meet the previously listed requirements without Darcy ever coming up to you afterwards to start the quest. In such a situation, you can enter 'SetStage 457c6 1' in the console to start the quest (this will not cause the quest to appear in your quest log). If you are unable to obtain the photo from Darcy, entering 'player.additem 0008a1fb 1' in the console will place it in your inventory.

While in Diamond City after completing Diamond City Blues, Darcy gives the Sole Survivor the Marowski heist photo. One can either show it to Marowski to tip him off that Malcom Latimer stole from him, or show it to Latimer to blackmail him.

Blackmailing Latimer

 * 1) Latimer will offer 400 caps for the photo, or 600 with a successful speech check. After handing over the photo, the quest ends.

Tipping off Marowski

 * 1) Go to Goodneighbor and show the photo to Marowski. He will give 500 caps. Alternately, if he knows about the Sole Survivor's involvement in stealing his chems, he will forgive them rather than insisting they pay restitution for the theft.
 * With a successful speech check, he can be convinced to hand over the caps before seeing the photo. If the Sole Survivor then refuses to hand over the photo, Marowski becomes hostile. If the Sole Survivor escapes Hotel Rexford, they can then sell the photo to Malcom, resulting in a total of 900 caps (1100 if the Sole Survivor passes the speech check to receive 600 caps from Malcom).  Marowski and Stan Slavin will attack the Sole Survivor on sight, but can both be killed without any negative consequence.
 * 1) Marowski will ask the Sole Survivor to kill Malcom Latimer for another 300 caps (400 with a successful speech check).

Once the quest has been completed, one can return to Darcy in Diamond City and choose whether to split the caps earned from the quest with her.