Crime writer Michelle McNamara dedicated the past few years to cracking the case of The Golden State Killer, a serial killer and rapist who was active in the '70s and '80s and is believed to have murdered 10 people. She was working on a book about the case.
Now, following McNamara's unexpected death in her sleep on April 21 at age 46, Oswalt and several of McNamara's friends are determined complete her book on the murderer's crime spree and identify the killer.
"She was obsessed with cold cases – with crimes that, despite mountains of evidence and witness accounts and man hours committed to puzzling them out, still remained maddeningly unsolved," Oswalt, 47, tells PEOPLE in this week's issue. "She could retell these stories and frame them in a way that made them feel immediate."
McNamara, mother to the couple's 7-year-old daughter Alice, wrangled "cold, brutal facts" and stomached awful memories from police and the victims, two things Oswalt says most people would shy away from.
"Michelle stared straight at them – the facts sorted by her supercomputer brain, the human stories teased out and given dignity by her endless compassion and empathy," he says. " She listened with patience and heart to every story, no matter how deep the wound it described."
McNamara's friends say she was able to win over law enforcement sources, sharing clues and impressing them with her knowledge of the many cases she worked on in addition to the Golden State Killer.
Paul Holes, a cold case investigator with the Contra Costa County District Attorney's Office, learned to trust and respect McNamara after she began publishing a series of articles on the Golden State Killer in Los Angeles Magazine, for which he was a source. He was so impressed by her dedication and skill that he came to consider her a full-fledged partner on the case.
After McNamara got her book deal, she met Holes in person the San Francisco Bay area, and they drove around crime scenes where the killer had struck.
"She was not just in this to write a book, but had an actual desire to know everything and wanted to see the case solved," says Holes. "That time with her changed my perception – she wasn't a journalist but was going to be one of us in the investigation."
Fellow crime writer Billy Jensen says McNamara recently texted him to say she had a lead on a possible suspect.
"A lot of tiny details in his favor," Jensen quotes her as saying in a tribute piece he wrote. "We’ll see. Have been here before. But God I would be so happy."
"She always said the thing she wanted most – more than a best seller or a TV series – was to sit across the table from the villain in handcuffs," Jenson tells PEOPLE. "And if we are able to finish what she started, I'm for sure going to bring a photo of Michelle, hold it up and and tell him 'this is the woman that found you.' "
As for Oswalt, he vows his wife's book will be completed and published as a tribute to her life and work.
"I got to spend 13 years with a great crimefighter and a unique mind. And I got to spend a decade married to her," he says. "Way beyond what I deserve."