On Tuesday, it is still not exactly clear what drove Shannon Lamb of Gautier to first allegedly murder his domestic partner and then drive 300 miles north and allegedly murder a history professor at Delta State University.

Of course we know there is no good reason, there is no justification for such violence and terrorism, but we wonder all the same. The curiosity is natural, and we expect news reports to explain as best they can what led to Monday’s violence.

Besides explanations, tragedies provoke talk of prevention. Did anyone know? Could the murders have been prevented? Again, 24 hours after the fact, we still don’t know.

But we know perfectly well that in too many pre-meditated killings of late, someone did know and there were warning signs.

On Saturday, the Washington Post published a chilling story that shed light on the June church massacre in Charleston, South Carolina. In the story, titled, “American void,” the Post reporter makes it clear that the alleged gunman, Dylan Roof, told his friends he was poised to do something terrible. He talked of driving two hours to the church. He showed his friends the gun he would use to kill nine people and he talked of doing “something crazy.” Yet his friends said nothing. Even when they saw the initial television reports of the massacre, when Roof was on the loose, they said nothing. True, it may be hard to imagine anyone, let alone a friend, would commit a horrendous act of violence, but it’s not hard to notice when a life begins to unravel. It is not hard to notice when a friend begins to articulate dark, dangerous thoughts or drink too much too regularly or act, just a bit, odder than usual.

After 9/11, we learned the now-common mantra, “if you see something, say something.” That goes beyond reporting the unattended bag at an airport. We owe it to ourselves and to each other to take care of our friends, and when someone we know begins to exhibit signs of self-harm or an intent to harm others, we need to say something. We need to tell mutual friends, tell parents or tell law enforcement, but we need to open up, before it’s a story in the paper.