Is "you shall know them by their fruits" a reliable test of true Christian faith in light of believers committing violent acts?

Jesus said in Matthew 7:16, "You will know them by their fruits." This verse is often cited to identify genuine believers based on their actions and character. However, a recent incident in Minnesota where a self-professed evangelical Christian—who had even received an appointment—was involved in the shooting of a congresswoman raises questions. How should this verse be understood in light of such events? Can we truly and reliably know a believer by their fruits, especially when someone outwardly identified with Christianity ends up acting in a way that seems so contrary to Christ’s teachings? How do different theological traditions interpret this principle when actions contradict profession of faith?