I received a rebuke the other day from a reader baffled by an approbatory review of Murder One, a worryingly addictive American crime series currently running on BBC2. (If you haven't seen it, the series follows a single celebrity murder trial over the course of 23 episodes, a scale that allows an unusual concentration on the minutiae of the American legal system.) The charge was a serious one: essentially, dereliction of duty - that I had failed to maintain the requisite critical vigilance. At first glance it looked bad to my rapidly assembled defence team - after all, much of Murder One is a bit risible, from the Formula One emoting of its star Daniel Benzali to the uncanny way in which the law firm he works at never seems to lose a case. It seemed unlikely that I would be able to hold up under tough cross-examination, even though I had been reasonably cautious in my initial review (no reckless use of words like "masterpiece" or "genius"). Faced with a tough question ("Murder One is a little preposterous, isn't it?"), I would either have to perjure myself or surrender the case right there.We decided to bargain. I would plead to a lesser charge of reviewing without due care and attention and my lawyer would advance mitigating evidence of long-term serial addiction - as part of the deal I would promise to check in to a thriller de-tox clinic and get myself straight.

And then, at the eleventh hour (just like in the movies), a vital new piece of evidence came my way. A copy of Christopher Darden's book In Contempt, about his role as a prosecutor in the trial of OJ Simpson, turned up in the office. Inside was tucked a note: "Read this. A friend." As I turned the pages, it slowly dawned that my case might not be hopeless after all, that if we called Darden for the defence I could just beat the rap.

In Contempt is itself a masterful piece of special pleading, an attempt to rescue something from the wrack of defeat and despair Darden felt when the jury finally returned a Not Guilty verdict. As an account of the racial tremors running through the trial, it is fascinating - Darden was under exceptional pressure as a black lawyer prosecuting a black hero, and using the evidence of the hated Los Angeles Police Department to do it. As an insight into the degree to which the trial was corrupted by media interest, it is also useful. But the book is flawed, partly by the evidence of Darden's volatile temperament - which the defence counsel Johnnie Cochran was able to exploit at will - and partly by its failures of taste. It opens, for example, with a grotesquely lurid apostrophe, to Simpson himself, imagining the killings in cinematic detail - "You came out of the shadows so quickly, so smoothly, you must've surprised yourself a little... You damned near cut her head off. It was freeing and painful at the same time, wasn't it? You had finally taught her to listen. What better listener could there be than someone you silenced for ever?"

This is pure storytelling, whatever the truth of the incidents it describes - it takes the imaginative devices of popular crime novels and turns them on a real event. In that sense it is a simple misjudgement for a man determined to prove that Simpson's defence clouded the truth with emotional "smoke" and who notes indignantly that one of the defence's main arguments was constructed by a "true crime writer". In Contempt is full of such hard- boiled touches, details more suited to pulp- fiction or film than to a legal memoir. "Since college, I have thrown back tequila on occasion," writes Darden, "usually when I needed a drink as hard and unforgiving as my thoughts." We owe these passages, I suspect, to Jess Walter - Darden's co-writer - but the fact that the author is happy to admit them is still revealing. It testifies (and this is where my Murder One defence comes in) to the irreversible contamination of reality by fiction in certain branches of American life. The policemen in In Contempt, for instance, have come straight from central casting: "He's lying like a rug," says an LAPD contact shortly after OJ's arrest. (One of the prosecution witnesses, it's worth remembering, was a policeman who had actually taken bit-parts in cop movies.) The gumshoe style is picked up by Darden: the defence came forward with an alibi witness, he notes, but she "would later fold like a cheap tent under our questioning".

Nor is it just Murder One's tough talk that is endorsed by In Contempt. The embarrassing emotional fluency of the characters in the television series, their readiness to get in touch with their feelings, is also reflected in Darden's book. This was a trial in which he and Marcia Clark exchanged gushy notes during hard times: "I am honored that you are my friend," wrote Darden in one billet-doux and, but for the scrutiny of the nation, things might have gone further - "I will say this," he writes of their friendship, "as spring melted into summer, I began to wonder what might happen away from the flash of tabloid photographers and television cameras." Murder One might be sentimentally hokey, then, and its lead character might be recklessly self-dramatising. But so is the world it describes in such fascinating detail. The defence rests.