"You did it, Michelle."

Comedian Patton Oswalt proudly and tenderly spoke those words to his late wife in an Instagram video on Wednesday.

Finally, an arrest had been made in the case of the Golden State Killer, a moniker Michelle McNamara coined on her personal mission to catch a man responsible for at least 12 killings and 50 rapes throughout California in the 1970s and 80s.

McNamara died in her sleep at 46 in April 2016. She had been in the middle of her hunt for the killer and her book, "I'll Be Gone in the Dark: One Woman's Obsessive Search for the Golden State Killer."

Oswalt helped finish the book after McNamara's death. It became a No. 1 New York Times best-seller.