The comedian’s life was upended in 2016 when his wife died. He discusses her role in the Golden State Killer case, the ‘shadow slog’ of grief – and the reaction to his remarriage

The sad clown. The chronic depressive comedian. It is one of the greatest cliches in showbusiness. Patton Oswalt – ebullient, life-affirming, swearing as he hurtles along the Interstate 10 highway in California – does not sound like one of those. At least, not any more.

Oswalt’s wife, the true-crime writer Michelle McNamara, died suddenly in 2016 at the age of 46. That was the second-worst day of Oswalt’s life. The worst was breaking the news to their seven-year-old daughter, Alice, the next day.

Three years later, Oswalt, aged 50, is healing. An atheist, he found salvation in single fatherhood. He remarried with no apology to trolls shouting: “Too soon!” His career flourished on stage, TV and film. And he is very excited about a European tour that finishes in London on 15 June.

Oswalt – whose CV includes The King of Queens, Ratatouille, Young Adult, Veep and the upcoming The Secret Life of Pets 2 – seems like a man firing on all cylinders. He and McNamara must have been quite a double act, everyone’s favourite dinner conversationalists.

McNamara was obsessive about unsolved crimes. She created a website, True Crime Diary, that covered breaking stories and cold cases, looking for new angles that police had missed. It may sound morbid to some, but not the way Oswalt recalls it.

Facebook Twitter Pinterest ‘She definitely put a lot more light back on [the Golden State Killer] case’ ... Oswalt with his wife Michelle McNamara at the premiere of Young Adult in 2011. Photograph: Gregg DeGuire/FilmMagic

“She was just a really deep storyteller, and really good storytelling is about solving problems – and all of your problems tend to be people,” he says. “So, with a true crime, especially a cold case, it was almost like the writer and humanitarian sensibility of her was offended that we have all this technology, we have all these clues, we have all this insight: why is this person not caught? And I think that ended up being something that really intrigued her.”

McNamara was animated by one whodunnit in particular: more than a dozen murders and at least 50 rapes in California between 1976 and 1986. Some had named the unknown perpetrator the East Area Rapist, others the Original Night Stalker. McNamara coined Golden State Killer and it stuck.

She was working on a book about the case, I’ll Be Gone in the Dark, at the time of her death. But there were two posthumous postscripts. Using her handwritten notes and thousands of files on her computer, Oswalt ensured the book was finished and published with the help of Paul Haynes, the lead researcher on the case, and Billy Jensen, an investigative journalist. Then, four days after the second anniversary of McNamara’s death, authorities announced that a 72-year-old man named Joseph James DeAngelo had been arrested in California after DNA evidence that linked him to the case was taken from a discarded tissue in his rubbish and the handle of his car door. He has since been charged with offences including 13 murders and 13 crimes related to sexual assault.

The breakthrough had taken 42 years. Does Oswalt believe that his wife’s work was responsible? “Don’t take my word for it,” he says. “Paul Haynes and the other homicide detective said she definitely put a lot more light back on that case and got a lot more interest and resources put back into it. I’m going to say an objectively proven yes on that one.”

When DeAngelo was arrested, the feeling was “obviously bittersweet”, Oswalt says. “I would have gone: ‘Off you go, I’ll take care of Alice. You’ve got work to do.’ But at the same time she would have gone: ‘I don’t care about credit. I just want to know [the perpetrator is] locked up. That’s all I care about. Both for the victims and just for the basic overall sanity of the reality that we live in, the guy should be rotting in jail.’”

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DeAngelo is awaiting trial. “Part of me would like to visit him, but I would only specifically ask him the questions that Michelle outlined at the end of her book. I wouldn’t have any deeper insight to bring to him than Michelle or these investigators did.”

The phrase Golden State Killer captures a California paradox: bright sunshine mixed with the pitted noir of Double Indemnity and Sunset Boulevard. Oswalt’s own natural light was dimmed on 21 April 2016 when he found McNamara in their bed, no longer breathing. Paramedics were called and pronounced her dead. An autopsy found she had an undiagnosed heart condition and had taken a mix of prescription drugs, including the amphetamine combination Adderall, the opioid painkiller fentanyl and the anti-anxiety drug Xanax.

Full of dread, Oswalt told Alice the next day. “I looked at my daughter and destroyed her world,” he recounted in his subsequent standup show, Annihilation, the second half of which describes the tragedy with searing yet humorous honesty. “I had to look at this little girl that was everything to me and take everything from her.”

Suddenly, in his late 40s, he found himself a widower and a single dad. He admits: “I can say with a pretty good amount of confidence that if I hadn’t had Alice, if I didn’t have a daughter, I think I’d be alive right now, but I don’t think I’d be functioning very well. Drinking would have been a problem. Binge-eating would have been a problem. And then, I think, old-fashioned, almost Victorian melancholy. I would have merely existed. I would have just eaten to live and then would have drunk so that I didn’t feel anything any more and then would have repeated it every single day. Having Alice was like: ‘I’ve got to get up, I’ve got to make breakfast, I got to take care of this little life.’ So, it’s almost like I had freedom from choice because I had our daughter.”

Facebook Twitter Pinterest ‘Part of me would like to visit him, but I would only specifically ask him the questions that Michelle outlined at the end of her book’ ... Oswalt on Joseph James DeAngelo, who has been charged in the Golden State Killer case. Photograph: Sacramento Bee/TNS/Getty Images

He continues: “The thing that people don’t tell you is, when you’re going through grief, every single thing that you do – no matter how mundane: making breakfast for your daughter, doing laundry – is part of your healing process, whether you want it to be or not. You are basically rebuilding your psyche, whether it’s in something ‘elevated’ like writing, or quotidian like paying bills.”

The “shadow slog”, as he has called it, also included counselling and reading A Grief Observed by CS Lewis; the author of The Chronicles of Narnia was also an influential Christian thinker. Not that Oswalt turned to God. Not for a moment.

“I wanted to give Alice more hope in the daily waking life than: ‘Oh, in some far-off make-believe world maybe we’ll see her in the clouds.’ That to me felt insulting to this very inquisitive, very precocious little girl that Michelle had raised to be very sceptical and smart and loving and compassionate. To just go: ‘Well, we’re going to believe in this fairytale and then just not think about it,’ ... I wouldn’t dismiss her curiosity that way.”

Was McNamara’s death a reminder of Oswalt’s own mortality? “I found consolation in stuff Michelle used to say to me because she was a true-crime investigator. One of the phrases she hated was when people go: ‘Well, everything happens for a reason.’ She’s like: ‘No, it doesn’t, it’s all random. If you want reason, if you want some grace in the world, be kind.’ The only reason and grace we have coming is whatever you put out there.”

Oswalt’s mother was a lapsed Catholic, his father “a kind of ‘meh’ Lutheran”. The fact that McNamara died, rather than Oswalt, only reinforced his view that there is no cosmic conductor.

“Let’s say I did believe that this was part of God’s plan. Well, then, what a shitty plan. You’ve got this true-crime investigator, this genius on the trail of these cold cases, and then a guy that tells dick jokes, and you’re going to take one of them and you take the crime investigator? That’s the stupidest thing on the planet.”

Facebook Twitter Pinterest ‘I feel we’re sounding alarm or despair to a Brit, but you guys have lasted so much longer under way more precarious conditions than we have’ ... Oswalt with Timothy Simons in Veep. Photograph: HBO

In July 2017, Oswalt announced his engagement to the actor Meredith Salenger. The reaction online was divided. Some offered congratulations and expressed delight that he had discovered happiness again. Others suggested he was remarrying with indecent haste. Oswalt gives that societal taboo short shrift.

“The ‘pushback’ I got was from anonymous people on the internet. With 90% of internet pushback, it’s not anybody actually morally outraged at anything; they’re just bored. One friend of mine got married nine months after his wife passed and everyone gave him shit. Another got married six years after his wife passed and people were like: ‘You waited too long. This isn’t real.’ So, there’s always going to be people who say: ‘I like you when you’re mourning because then I’ve got this little lamb that I get to take care of. How dare you move on?’ I feel like I’m only living this life. I don’t owe anyone else anything else.”

Virginia-born Oswalt, who is the son of a US Marine and was named after the second world war general George Patton, has been equally pugnacious when talking or tweeting about politics. But unlike garrulous Hollywood types such as John Cusack, Robert De Niro and Rob Reiner, he has grown weary of being asked about Donald Trump.

“He’s terrible for comedians,” he says. “What is the point? He does not give a shit. You can’t do jokes about someone who is not connected to humanity or shame or anything other than immediate, libidinal pleasure. That’s all it is for him. It’s whatever is literally in front of him. It’d be like trying to shame a shark or a tornado. They’re just like: ‘If it’s in front of me, I’ll eat it; if not, I’ll swim till I see something else to eat.” Shamelessness is Trump’s superpower? “It kind of is. It’s his Green Lantern ring.”

Yet Oswalt remains fundamentally optimistic about the future of the country, “if only because I’ve read so much American history and I’ve seen how much closer to the brink we have been as a nation. Also, I feel we’re sounding alarm or despair to a Brit, but you guys have lasted so much longer under way more precarious conditions than we have. You’re like: ‘Oh, you adorable Americans with your: “Oh my God, this is the end of America.” Why don’t you guys take a deep breath and read some British history? We’ve been way closer to disaster than this. So, not to use the old cliche, but Keep Calm and Carry the Fuck On.’”

It is a principle that Oswalt applies to his own life. He found love again. His daughter, Alice, is now 10. He is on tour and his screen career is going great guns. The trauma of 2016 is in the rear-view mirror. But it will never be gone.

“I don’t think of it as often as I did,” he says. “This is what I’ve heard in my grief group: you think of it less and less every day of your life, because that’s how healing works. There are times when a snippet of a song or just a feel in the air will remind me of her. That will always be there. But life forces you to move on whether you want to or not.”

Patton Oswalt is at the O2 Forum Kentish Town, London, on 15 June