Patton Oswalt is "so proud" his late wife's book is on the New York Times bestseller list.
"I hope you know, sweetie. I feel like you know. And I hope you know it when your work leads to his capture," Oswalt wrote, referencing McNamara's research about the Golden State Killer in the book.
"#IllBeGoneInTheDark debuts at #1 on the @nytimes bestseller list. I'm so proud of you," he said.
McNamara died at age 46 in April 2016 from an undiagnosed heart condition and complications from prescribed medicine.
"I wish I could tell you some moment of epiphany when I realized that I was going to finish it, but I don't have it," the actor told Entertainment Weekly last week.
"That whole year is just this really painful blur."
Oswalt and McNamara were married more than 10 years, and share 8-year-old daughter Alice. The comedian got remarried to Meredith Salenger in July.