After you kill Northy, or more accurately, he seems to kill himself, you're supposed to check the body for clues. With the Silver Shroud missions you have to toss a calling card onto the character's body after you kill them to register as complete.To complete the look, he asks the player character to find the Silver Shroud costume at the TV production studio in the Hubris Comics building. The best path to make sure that Kent lives while subduing all the enemies is to role play as the Shroud through all conversational options. Go to the Memory Den and speak to Kent Connolly and agree to find the Silver Shroud Costume. A Persuasion check can be passed to get some caps upfront. I've killed Northy in the silver shroud quest and must search the body. There is a marker on a pile of rubble, but I don't see any way to get under. In the room beside a memory lounger to the west in Goodneighbor's Memory Den building, you'll find a ghoul named Kent. Goodneighbor and get back to playing the Silver Shroud to entertain old Ghouls.