I suppose this scenario is actually somewhat reassuring, because the guy who killed 12 people deserves whatever misfortune falls upon him. You wouldn't have to feel bad stealing his knowledge and memories, and could also go to the local guards to turn him in with the knowledge you've obtained.
Though good luck sleeping at night with the knowledge of what it felt like to murder 12 people with your own hands and see the life fade from their eyes.
The way he reacted makes me think that not just the memory that he killed people was taken, but the desire to as well. Otherwise you think he'd be more like "I don't remember doing this, but cool!"
There's an interesting philosophical debate there. What good does imprison a guy who have no recollection of doing the crime, or the circumstances around them? Can be argued that the person who committed the crime and this guy finding the bodies are two different people who share the same body.
I'd go looking for another mindflayer offering "spotless mind" services and pay to have those memories removed. Assuming they can be trusted, of course. The hard part being that they're still mindflayers.
Kinda reminds me of a few Sci-Fi settings- Altered Carbon has people that enjoy murdering people, and since people can swap bodies freely that sort of thing is easily done. There's an explicit difference between 'sleeve death' and 'real death', even legally. Killing someone's sleeve- or body- is a crime, but it's not murder anymore. If you actually destroy the lil chip that actually contains the person, that's 'real death'. Man I love that show. S1, at least.
Alternatively, Cyberpunk with it's braindances could cater to an extremely similar audience.
The carpenter killed them, and forgot he did it with the transfer. Really, I think the woman shouldn't consider it her crimes but I guess some confusion is understandable under the circumstances.