Iowa police announced this week what we long suspected: Mollie Tibbetts, the Iowa college student who was missing for over a month, is dead. The preliminary autopsy report, released Thursday, reveals that she was killed by “multiple sharp force injuries.” Prosecutors have filed first-degree murder charges against Cristhian Rivera, a 24-year-old Mexican who had been working at Yarrabee Farms in Brooklyn, Iowa, since 2014. The police say that Rivera is in the country illegally — though this has been disputed by his lawyer — and that he presented fraudulent identification to his employer when he was hired. Anyone really interested in understanding why Trump was elected president should pay careful attention to this episode.

We don’t yet know for sure if Rivera is guilty, but the tragedy of the scenario painted by the charges is explosive. The way many people see it, if a foreign national, apparently in the country illegally, kills an American citizen, it underscores the urgency of Trump’s message of putting Americans first. In other words, the murder of Mollie Tibbetts was not only ugly and evil, it was unnecessary and utterly preventable by government action.

Some supporters of amnesty for illegal immigrants already in the country, as well as increased legal immigration, don’t seem to be able to acknowledge the reality of Tibbetts’ murder. Senator Elizabeth Warren is a case in point. Rather than admit during a CNN interview that our failure to enforce our immigration laws and control the border contributed to Tibbetts’ death, she changed the subject. After saying that she was “so sorry for the family here,” Warren argued that “we need an immigration system that is effective, that focuses on where real problems are,” in effect casting those crossing the border illegally as the “real” victims.