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.
Oswalt helped after her death to finish and publish the book, which hit shelves Feb. 27.
"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."
"It was her book and it's an amazing book. I wanted to do right by her," he explained.
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.