Every reader of The Mushroom Tapes will open the book knowing that Erin Patterson was found guilty in July of murdering three people – her in-laws, Gail and Don Patterson, and Gail’s sister Heather Wilkinson – and of the attempted murder of Heather’s husband, Ian Wilkinson. They will also know she was sentenced to life in prison with a non-parole period of 33 years, and is now appealing against her conviction. Who among us hasn’t been roped into speculation about this family tragedy, the carcass of which has been picked over by pundits, amateurs and experts for years now?

Over 10 long weeks, the baroque details of the trial of Erin Patterson were made immediately available to a ravenous public – including sightings of Helen Garner, Chloe Hooper and Sarah Krasnostein, three of Australia’s most celebrated nonfiction writers, in the public seats of courtroom four in Morwell, Victoria. Were there several works of Australian literary nonfiction about Erin Patterson in the offing? A week after the guilty verdict was handed down, Text Publishing announced that the trio would collaborate on a book: The Mushroom Tapes.

I approached this book with a fair dose of scepticism. Two major books on the trial have already been published, with more to come. Didn’t the bereft families deserve some peace? And why the rush? Did this book really need to be written in time for the Christmas sales period?

A similar mixture of compulsion and resistance afflicts the authors of The Mushroom Tapes: “People say to us, you must be going. No, we answer. No. No. No.” But they do go to Morwell. “The current of the story,” they write, “has a stronger pull than we had expected.”

Garner, Hooper and Krasnostein appear in the book as Helen, Chloe and Sarah. Their collaboration was conceived as a podcast and much of the book is drawn from transcripts of conversations recorded while travelling between Morwell and Melbourne. They are often on the road but never able to stay in Morwell for long. The result is a work of oral literature that has been yoked to the page; conversations between friends, conversations between women. At one point, Garner says: “If anybody wants a mandarin or a biscuit, just kindly scream out and I’ll pass it over.” In a different book, such asides might have been edited out. Here they signal an interest in the ephemera of daily life, in the nourishment required to sustain conversations, friendships and families.

In both their rhythm and register, these intimate conversations recall the forms that mediated Patterson’s trial: podcasts, panel discussions, social media threads, group chats. We talk to make sense of the world – and everybody has something to say about Erin Patterson. “People are obsessed,” Hooper writes. “I run into someone at my kids’ sport, or the hairdresser, or wherever – they’re either listening to two podcasts a day and know more detail about the trial than I do, or they’re equally as strongly repulsed.”

And so we find ourselves in the car to Morwell with these three intelligent women as they try to figure out what is going on in the courtroom, and how the hell Erin Patterson got there. Marriage, class, sex, money, mushrooms, women and their lives – our lives.

The transcripts have been carefully edited, but locutions that convey the immediacy of live commentary are retained: “Sarah, you’re a lawyer, why has Erin decided to hold her trial in Morwell?” Sometimes it’s a bit too much like reading a podcast transcript. We stay in the present tense in the reported sections that break up the transcripts as well: “She sits in the dock at the back of the courtroom, flanked by two custody officers.” It’s as if the trial were playing on a non-stop loop. Two-podcast-a-day readers may relish the effect, but I found stasis, rather than suspense, in this unrelenting present tense.

Fleeting disagreements between the authors are captured in the transcripts, and so is their equivocation:

Chloe: Are we really going to drive past Erin’s house? I feel unsure about this.

Sarah: For me, it’s a normal part of doing research.

Helen: We’re not knocking on anyone’s door, for God’s sake.

There is a lot of driving past significant sites in The Mushroom Tapes, and many such self-exonerating exchanges. The first line of Janet Malcolm’s classic study of crime journalism hangs over these conversations: “Every journalist who is not too stupid or full of himself to notice what is going on knows that what he does is morally indefensible.” The authors of The Mushroom Tapes certainly know this. Often it is Hooper who voices her qualms most strongly. At one point she says: “This trial is being used for public entertainment. I feel squeamish about joining the pile-on.” And yet, here is the book.

The authors give the victims of the murders their due, and they write with great compassion about the unnamed children of Erin and Simon Patterson; “they’ve been handed this bag of stones that they’ll carry for the rest of their lives,” says Krasnostein, one of the book’s most memorable lines.

It is Erin Patterson, however, who captivates them. Patterson bounces, says Krasnostein, “between smallness and grandiosity”; Hooper notes that she “radiates discontent”. In an early conversation, Garner says, “It’s not that I’m big-hearted or anything, it’s just that I have this awful feeling – that could be me.” It’s quickly established that Patterson is not, in fact, much of a stranger at all; the authors write “we have discovered that the three of us are variously connected to Erin Patterson and the wider family”. After taking in Patterson’s time in the stand, Garner observes that “the gap between her and me shrank down really small”.

This combination of personalisation and projection is now omnipresent in the culture. It is why I found it ultimately difficult to extract The Mushroom Tapes, for all that it is extremely readable, from the rest of the chatter about the Patterson case. Garner, Hooper and Krasnostein are an acute trio of conversational partners. Their precise, wry observations compel the reader’s attention – but so did all the loud headlines and live-crosses that kept this calamity in public view.

In its formal commitment to immediacy and intimacy, not to mention its speedy publication schedule, The Mushroom Tapes reflects the moment in which it was written. I wonder whether a collaboration that had been allowed to develop more slowly might finally have relinquished the present tense, and put this case in the past. As for whether this is the last word on the Patterson case, certainly not. A series of conversations across Australia with the authors of The Mushroom Tapes sold out well before the publication date of the book. The talk about Erin Patterson, it seems, is not likely to stop soon.

• The Mushroom Tapes is out now in Australia (Text Publishing, $36.99) and will be published in the UK on 20 November