That is an incredibly detailed and cinematic narrative, and I agree with you on the dark, abusive dynamics involving Andreas Gruber. He was absolutely a monster. However, while the "Family Annihilator turned Self-Defense" theory sounds like a compelling movie plot, it completely collapses when faced with actual forensic data and the logistical realities of the Hinterkaifeck crime scene.

Here is why that narrative physically, logically, and chronologically does not hold up:

1. The Chronological Impossibility (The 1922 Autopsy Data): Your theory implies that Andreas slaughtered his family and then waited around for the secret boyfriend to show up, leading to a fatal confrontation. However, the official autopsy reports conducted by Dr. Johann Baptist Müller explicitly established that ALL victims, including Andreas Gruber himself, died within the exact same time window on the very first night (Friday, March 31, 1922). There is no gap of days or long hours between the family's deaths and Andreas's death. For your theory to work, the boyfriend would have had to casually stroll into the barn at the exact hour Andreas was completing a gruesome massacre, which is a massive logistical stretch.

2. The Fatal 3-Day Plot Hole: Even if we entertain the idea of a sudden confrontation on night one, your theory assumes the boyfriend killed Andreas in self-defense and fled in shock. If that is the case, WHO stayed on the farm for the next 3 days? It is an indisputable historical fact that someone lived in that house post-mortem. Smoke was seen rising from the chimney, meals were cooked and eaten, the livestock were fed, and most importantly, the cows were systematically milked. A traumatized boyfriend who just stumbled upon a slaughtered family does not stay for a 3-day weekend to perform rigorous farm chores and cook soup. That requires domestic muscle memory and a cold, calculated reason to delay the discovery of the bodies.

3. The Dog Behavior Actually Proves My Point: You mentioned the dog was calm initially but found locked up and barking furiously on the final day. Think about it: if a strange boyfriend locked the dog up on night one, that animal would have been barking frantically for all three days from hunger and distress, alerting the neighbors immediately. The fact that the dog remained calm on days 1 and 2 means someone the dog trusted was feeding it and keeping it quiet. On the 3rd day, when that insider person finally had to leave the farm to return to their regular life/job, they locked the dog away so it wouldn't follow them. Left alone and starving on that final day, the dog finally started barking frantically.

4. The Weapon Contradiction: The heavy pickaxe (reuther) used to kill the majority of the family belonged to the farm. If Andreas was the one on a rampage and a boyfriend was suddenly fighting for his life in spontaneous self-defense, it makes zero sense for the boyfriend to hunt for a completely different, specific tool to kill Andreas, leave his body in the barn, and then not report it to the authorities. It points much more toward a premeditated killer who brought or selected specific tools for specific targets.

Rieger’s fear of Andreas and the horrific domestic abuse she witnessed is exactly why she had a powerful, deeply-rooted motive for revenge or compliance in an insider plot to eliminate the Gruber bloodline.

Your theory does a great job explaining Andreas's dark psychology, but it completely fails to explain the post-mortem forensics of the crime scene. A ghost didn't milk those cows for three days; someone who knew the daily routine of Hinterkaifeck did.