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Last year, 5,590 Indigenous women were reported missing to the F.B.I.’s National Crime Information Center, but advocates say the staggeringly high rates of violence suffered by Indigenous people are still not fully reflected in official accounting. Some of the victims are misclassified as Asian or Hispanic, or are overlooked if they live in urban areas instead of reservations, or their cases are lost in a jurisdictional maze over which state, federal or tribal law enforcement agency bears responsibility for investigating.

Law enforcement officials said that these can be extremely difficult cases to investigate, sometimes ranging over vast expanses of territory, but that they are committed to solving them. The families say the problem is more a matter of will and resources than of difficulty.

“Native women have been dehumanized from the very beginning,” said Desi Rodriguez-Lonebear, a demographer who grew up in Big Horn County and is on the board of the Sovereign Bodies Institute, which has created its own database of cases. “The law has failed us time and time again. We’re tired of it. We’re tired of our people dying, of our kids going to jail.”

Now, families like Selena’s are taking an urgent public stand to pressure politicians and law enforcement to provide more aggressive responses to these cases. They are raising alarms through social media and even bracing themselves against Montana blizzards to keep their loved ones from being forgotten. They are organizing candlelit vigils, rallying at courthouses and sheriff’s offices and marching for days along prairie highways, reservation roads and to the steps of state capitols.