And now, an Illinois addition to the list of mass shootings that agonize all Americans on somber anniversaries — and that agonize survivors and the families of victims every day of the year. This week already had delivered anniversaries of the Northern Illinois University shooting in 2008 and the Parkland, Fla., high school shooting in 2018.

Friday’s bloodshed was at the Henry Pratt Co., a valve manufacturing firm in the western Chicago suburb of Aurora. The casualty count that authorities disclosed Friday evening — six civilians killed including the gunman, five police officers wounded by gunfire — adds still more families to what Gov. J.B. Pritzker termed “a group that should not exist yet continues to grow.”

What might the death toll have been if police hadn’t responded within four minutes to 911 calls and hustled into the 29,000-square-foot facility? Unknown, thankfully. We’ll echo Aurora Police Chief Kristen Ziman’s public message to her officers: “Thank you for running toward gunfire.”

The damage these mass shootings cause, beyond the carnage and casualty tolls, is incalculable. They occur so frequently that we Americans have factored them into our culture. In everyday life we now acknowledge a risk, an expectation even, that at any moment gunfire may shatter normality.

Schools, churches and offices all might be targeted, so every well-prepared student, congregant or worker cases buildings for escape routes and hiding places. Safety drills must be scheduled. Children must be introduced to the idea of facing gunfire so they know what to do if it happens.

Like the school shootings that began with Laurie Dann’s assault on a Winnetka elementary school in 1988, the workplace shooting is a recognizable phenomenon here. Among the most notorious: Many Chicagoans still live with the horrors imposed by William Baker, who killed four co-workers and himself at a Navistar International factory in Melrose Park in 2001. And the comparable horrors imposed by Salvador Tapia, who killed six former co-workers at a South Side auto parts warehouse before being shot by police in 2003.

And now Aurora. Early speculation about a motive centered on a workplace issue, but we can’t know whether the catalyst was one person’s despair or self-pity or aggression or something else. This killer takes the demented logic of his plot with him to the grave. We profoundly wish he had not taken innocents with him.