Trying to recall a film based on one main scene

I’m trying to recall a movie I mostly remember one (significant) scene from.
That scene, which sets the tone for the entire film, probably takes place before it even reaches halftime. A young white man with short hair - late teens, or early twenties - sits in his home’s living room with his parents. At some point he leaves the living room - and returns with a rifle and kills both of them, and possibly also his brother or sister in another room. He then leaves the house and goes on an escape journey. It may be a veteran who returned from the military with PTSD; It is possible that he kills only two of his family members and not three; I’m not sure. I remember there was an exposition before this scene; You can see that he is a quiet and a bit strange guy. Then comes this scene and it’s revealed how disturbed he is. Another thing I remember is that there is a storyline that runs parallel to his storyline. Perhaps of an investigator or police officer who will eventually be on his trail; Maybe something that doesn’t seem related at first but ends up intersecting with the plot of the disturbed guy.

It is almost certainly a film from the eighties or early nineties. One hundred percent before 1993. And it is a thriller or a drama or an action film. Certainly not a comedy, and certainly not a film that involves any supernatural elements.

Sounds like Targets (1968):