Keith LaFountaine’s review published on Letterboxd :
There is a fundamental question at the center of Blue Caprice that, while discussed extensively, is never answered:
It is easy to pull some basic assumptions or deductions from the narrative we are shown here, but the truth of the matter is that we will never truly know exactly what happened in 2002. The official statements from the perpetrators push the narrative that they were trying to "shut things down" across the U.S., but it has never been explained in more detail, and even that explanation is hazy in its own way.
The point of this film, in my mind, is not to divulge the objective truth of the situation that led up to the D.C. sniper attacks, but instead to explore the idea of evil: what makes a person evil; or, at the very least, what pushes someone in the direction of doing evil things?
In the film, Lee is influenced by a variety of factors, from his poor relationship with his mother, to John's mentoring, to Ray's affinity with weapons, but there is nothing apparent that makes all of these things click. Sure, his relationship with John, and their perverse father/son relationship, could have been a large proponent, but plenty of people - myself included - would not commit heinous acts like this to appease our biological parents, let alone semi-surrogate interpretations of parents.
This then leads us to a discussion of mental illness, of which I am not qualified to discuss in-depth.
Regardless, I don't necessarily subscribe to the notion that Lee's actions were entirely motivated by his relationship with John, as the film's final moments would insist we pursue as a line of reasoning. But, as I said, I don't think the film itself is trying to give a definitive answer, which is not only more robust from a philosophical standpoint, it also makes for a more interesting film.
The real issue with this approach in Blue Caprice is that the film itself is so cold in its tone and atmosphere that it's hard to really connect with anybody, or anything, in the film beyond surprise and shock in the moments where those emotions are called for. While intimacy with these characters, from a viewer's perspective, may not enhance the overall experience of the narrative, it also may lead to some more interesting questions of relationships and actions.