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.

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.
 * 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.

Bugs

 * If you refuse to hand over the photo to Marowski after getting paid, the Marowski Heist quest is still active, but has no objectives.
 * If you bargained for 400 caps for killing Latimer, you still only get 300 after returning to Marowski.