it the author sums it up quite nicely.
https://www.nationalreview.com/2018/08/mollie-tibbetts-murder-illegal-immigrant-crime-especially-painful/
"The murder of Mollie Tibbetts or Kate Steinle can be particularly hard to take because of a simple, anguished declaration. The murderer wasn’t supposed to be here. I’m reminded of the pain that people feel when, for example, they find out (in different crimes) that the police didn’t follow up on a lead or a prisoner was wrongly released on parole. The feeling is palpable"