Cyberpsycho House on a Hull won’t complete

So I think I screwed up. Earlier in the game I did the house on a hill mission. But I searched the area and never found the psycho. Oh well I’ll go do other missions and come back to it. Came back over and over. No matter what, I can’t complete it. It just says “Find the Cyberpsycho”. But there’s no one left. Watching a video I of a walkthrough I think I found my problem. When I first snuck onto the property I saw a dude in the garage. I sniped him with one shot before the boss battle triggered. I think that was the psycho and I killed him but didn’t trigger the completion of the gig. I got the rest of the cyberpsycho missions completed. Any way I can make this one complete? Restarting from a previous save won’t work as I’d lose tons of progress. I’m on a PS4.