What I can tell you is this: he was in the police for 10 years where he investigated a wide range of cases including drug manufacture, child abuse, corruption, serious violence, rape and murder.
He attended Westlake Boys' High School, is now in his 30s and works for a "government agency"; he's fit, lean and personable and he's written during the last two-and-a-half years - (sometimes a paragraph a day after work) - one hell of a cop novel.
It's an insider's view that deals with the real and tragic consequences of drugs, crime and abuse, on criminals, victims, families and cops.
Blackwell's intention was to bring a sense of realism to a genre where writers often sidestep workday realities in favour of big thrills and swift plot progression.
His strategy was to give the book over to one cop - Matt Buchanan - a widowed, damaged, but diligent detective who has been in the job too long.
If Buchanan's first-person account of life on Auckland's mean streets is sometimes indistinguishable from Blackwell's - "Nearly every adult I'd ever met in the course of my work who had serious anger, personality or drug issues had been abused as a kid. Physically, sexually, emotionally - or a combo" (Buchanan) - it's a frisson that, for the most part, works. Even when Blackwell touches on real life cases, such as the Jane Furlong investigation.
When a police psychiatrist diagnoses Buchanan as a "highly functioning depressive", he nods, goes home and downs the prescribed anti-depressants with bourbon.
Buchanan is a smart, diligent cop. He knows there's something very wrong with him but just trudges on regardless.
"... you have to be the professional. You maintain your composure. That's what everyone expects. So you cut away from the brutality, the blood, the bodies, the trauma, the pain -- job in this box, emotions over here in this one. Then you bury that box. You bury it deep."
It's dark stuff and Blackwell likes it that way.
"I watched the first season of True Detective and I liked how that was negative until the very last moment, and I hadn't seen that in a movie or novel before. I knew it would turn some readers off, but I wanted to put out something that was different and realistic."
The next 300 pages of The Sound of her Voice chart the results of years of dealing with the worst crimes imaginable.
As a cop, your job is to be the sounding board, the voice of hope, the link between them and the wheels of the legal system. It's a very tough, long process.
Bad guys get away, the court system lets victims down - homicide investigations proceed at a snail's pace.
"It sure wasn't as glamorous as TV pretended" ponders Buchanan at one point, "And the main characters were a shitload uglier too". (There's a nice streak of black humour running throughout the book.)
It was after reading Simon Wyatt's 2016 thriller The Student Body (Wyatt was another detective who Blackwell served alongside) that he thought about trying to get the manuscript published.
In person, Blackwell's smart and focused - not unlike his fictional detective Matt Buchanan - but the tortured hero of the book is a carefully controlled construct masking a life in turmoil.
"No, no, Matt's not me, although he's definitely based on experiences and people I've met in my career. I never felt the need to seek any help for trauma. I never suffered PTSD. I still love the police and everything about it and would go back if this job doesn't work out," says Blackwell, who has seen his fair share of cases go south in the courtroom, a fact he portrays powerfully in the novel.
He says he admires the detective programme here, and believes it one of the best in the world - ("It'll give the FBI a run for it's money").
"As a cop, your job is to be the sounding board, the voice of hope, the link between them and the wheels of the legal system. It's a very tough, long process. I think I've tried to bring that out in the book. I definitely worked harder on those cases than anything else, because you get to know those people. You see them take the stand to give evidence, holding it together, giving it everything. And then the lawyers break them down. It's horrible."
And it turns out that the bad guys aren't much different from the rest of us. A likeable police informant, Pete, in the book is based on the crims he's met while investigating Auckland's meth trade.
"They get hooked on meth, can't afford it, start dealing it, then learn how to cook it thinking they'll be able to do it for themselves. But then the gangs come knocking at the door and say 'hey you're going to cook for us'. Most of these guys are normal people, they have tradie backgrounds and get into it because a lot of the chemicals used in the process they are familiar with.
"They're trapped and don't see any way out of what they're doing. If they were to go on record and stand up in court they know they'd get a hiding or worse -- so a lot of drug informants are meth cooks and dealers. They're pleasant people to talk to, strange as that may sound. They've made a lot of wrong decisions and end up in a downward spiral. They're usually bottom of the chain; they take the big risk, and face life in prison if they get caught and it's very dangerous health wise.
"There's threats from police, threats from the gangs - it's not a good place to be, and nobody really wants to be in that situation."
I ask him if writing the novel was therapeutic.
"It didn't start off that way. The initial thought was to portray the CIB realistically; in a way that it hadn't been shown before. But while writing the book I was able to get out my frustrations with a lot of things like the court system and the laws around meth." Blackwell's in favour of decriminalisation and treating addiction as a health and education issue.
"I think the public have a misconception around the police. Most police hold the same views as the majority of the New Zealand population but they have to operate by the law."
"In many ways, Matt Buchanan's the opposite of Jack Reacher," he says.
"Reacher doesn't have to play by the rules but cops do. My goal going in was not to sell books but to show how cops think in their heads. I didn't want to clean it up too much, because cops aren't robots and that interior voice is often at odds with how they do their job."
