In Catch the Sparrow: A Search for a Sister and the Truth of Her Murder (Bloomsbury, Feb.), Rear probes the death of a stepsibling, Stephanie Kupchynsky, a music teacher she never met.

Can you explain the book’s title?

One of the most striking images for me when I started writing was of Stephanie’s pet cockatiel sitting on her violin bow. She could have just flown away at any moment, but she stayed. Birds are such fragile things, like Stephanie was in many ways, so I always wanted bird imagery in the title. Catch the Sparrow is a reference to a Crosby, Stills, and Nash song I have always found poignant. What’s lovely to me about its lyric—“How can you catch the sparrow?”—is that it implies an impossibility, and nevertheless a longing, for something that ultimately can’t be possessed. It often felt like I was on a chase for something elusive when I was writing the book—a sisterhood, an understanding, a release.

What surprised you the most as you investigated?

It was entirely unforeseeable how much I would find myself involved in attempting to understand the mind of a killer. Understanding psychopathic evil is like stepping closer to a Seurat painting and then stepping back, and seeing the full picture and all of the little points that comprise it, all at once.

What was the hardest part to write?

How some of the rampant corruption in the police department in Greece, N.Y., where Stephanie last lived, might have impacted the case. The long, twisty narrative of political endorsements and favors and alignments and flat-out crimes seemed very important to me. It was an arduous process of rewriting and revising to keep the focus on Stephanie and her case—and how I truly believe that in a different sort of atmosphere, things may have gone differently.

As an abuse victim yourself, how do you understand the vulnerability of even articulate, capable, and intelligent people to abusive partners?

Being an articulate, capable, and intelligent person doesn’t preclude anyone from being susceptible to abuse, just as being articulate, capable, and intelligent doesn’t preclude anyone from being an abuser. In my case, these things actually contributed to my personal propensity to connect with abusive people. Temperamentally, I’m likely to belabor arguments, and facing someone who won’t back down from disagreements is a surefire trigger for an abuser—at least in my experience. The trap I often fall into is that I think I am smart enough and loving enough to somehow conjure the magic words that will finally reach my abuser, and change him.