In Two Truths and a Lie: Murder, Obsession, and Justice in the Sunshine State (Random House, Dec.), McGarrahan, a reporter turned PI, seeks the truth about a 1976 double murder.

Would the question of whether there was a miscarriage of justice have obsessed you less had you not witnessed Jesse Tafero’s execution by electric chair for the murders?

Yes, absolutely. We all read terrible stories in the news all the time, but it’s the events we actually see ourselves that seem to matter most urgently. I was a young reporter when I witnessed Jesse Tafero’s botched execution, and for years and years afterwards, the flames and smoke of that morning came back to me every time I read or heard his name. Ultimately, that wasn’t something I could live with, and I had to write this book.

In retrospect, are you surprised at some of the risks you took in pursuing the story?

When I set out on my quest to find the truth about Tafero’s guilt or innocence, I honestly thought it would involve reading through some dusty old court files and then going to talk to a handful of witnesses. I definitely did not expect to land, Florida-style, in a cocaine backstory of drug dealers, jewel thieves, go-go dancers, and chaotic violence, and especially because I was doing this investigation alone, on the ground, door-to-door, face-to-face, it did at times feel risky to me. Tafero’s case is the most personally treacherous investigation I’ve ever done. If I’d known what it would ultimately involve, I’m not sure I would have been brave enough to try. However, once I got in, the only way out was to go right through to the finish, no matter where it led.

What was the hardest part of translating your quest for the truth about what happened into a narrative?

Investigation reports tend to be dry, so turning my thousands of pages of case documents into an actual story was a challenge. The main difficulty I encountered, though, was writing about myself. I’m a private detective—the word private is right there in the job description. It was only after a whole raft of failed drafts I realized that the story of this case was my story, too, and that if I wanted to really tell it I was going to have to dig into and understand my own part of it, as frightening and impossible as that felt to me. I had to finally figure out some things about my own life that I’d tried hard to forget a long time ago. That was difficult. It was also incredibly valuable, and I’m glad now I had to do it.