Well.
It isn’t a “lesson” that they even want to “learn”. They know full well that it isn’t important who did what, it is important that they use the occasion to smear.
When the truth comes out, it comes and goes, but they know full well the smear remains. That is why they do it. They aren’t shamed or embarrassed by it.
It is fully intentional.
If you look at the shootings of the past, the leftist smear is what you remember, not the truth.