Preet Bharara earned the unwelcome but perhaps heroic distinction of being one of the first federal employees to be fired by President Trump. But as US Attorney for the Southern District of New York (SDNY) from 2009 to 2017, he oversaw the investigation and litigation of all criminal and civil cases and supervised an office of over 200 Assistant US Attorneys. Following his “involuntary career change”, he became a Distinguished Scholar in Residence at New York University’s School of Law, and has used his time well to write about his career and some of the notorious and extraordinary cases in which he was involved. In particular, he writes eloquently about the ethics and priorities of the state and federal prosecutor, whose primary task is to serve justice, not simply to win convictions at any cost.

“Despite the portrayals in film, TV, and popular fiction, cops and prosecutors do not exist to put people in prison. They certainly exist to hold people accountable as appropriate, and to protect the public, but their job is to make sure justice is done.”

Patience

He writes about the importance of asking even basic questions without being afraid of appearing stupid, of keeping an open mind and not allowing confirmation bias or easy assumptions to limit the scope of investigation, of being humble enough to learn from your mistakes, and about the need for patience under pressure:

“After a horrible disaster or a violent crime, the world understandably clamors for accountability; they want the bad guys caught. The victims have faces; sympathy and empathy naturally flow forth. It’s understandable that people want to see the faces of the evildoers. They want culprits and they want them fast.”

Keeping an open mind at the investigation stage means forgetting about the presumption of innocence: potentially anyone could be guilty. But you need to tread carefully, not pounce until you are sure. Be prepared to change your mind. Be prepared even to walk away and not proceed. But once sure of your ground you should be fearless in proceeding, even when it rocks the boat or involves bringing down the rich and powerful.

When the truth is finally uncovered, it is often the least expected result. The socialite investment adviser turns out to be a multi-million-dollar fraudster. The privileged sons of millionaires turn out to be their killers. The convicted killers in other case turn out, on reinvestigation, to be the innocent victims of a corrupt or bungled police investigation. The badge-wearing cop is a would-be cannibal.

Teamwork

On the dynamics of teamwork, Bharara notes that “no leader does the job alone. Everything is a partnership, and if you don’t choose your teammates well, all hell will break loose.”

Among the team members he recalls, there is the ‘mob-buster’ Ken McCabe whose willingness to live in that world and collect the pieces to complete a criminal puzzle over the years helped topple godfathers. “If you really want to learn about fish, you have to live in the water, and that’s what Kenny did.”

Another is John O’Malley, a rigorous investigator with a photographic memory, whose “steel trap mind” recalled details about an apparently solved case that helped exonerate the wrongly convicted victims of an earlier investigation and find the true culprit.

Evidence

The worst mistakes are often made within the well-meaning margins, by smart and competent people who on occasion fall below their high standards. An example is given of the fingerprint evidence which, after the 2004 Madrid railway bombings, appeared to finger an entirely innocent American Muslim living in Oregon. Science may be foolproof, but it may not be proof against a well-meant reluctance to challenge apparently corroborated conclusions. In that case, the American analysis was challenged by the Spanish analysts, who identified the true suspect, an Algerian national, and the American suspect was exonerated.

One of the best chapters is about obtaining confession evidence. “Soft words do more than hard blows,” says Bharara. He cites the example of Hanns Joachim Scharff, a German working for the Luftwaffe during World War II, whose patient techniques worked far better than the gross brutalities of the infamous Gestapo interrogators. “The best evidence shows that nothing useful comes from torture.”

It doesn’t even work with terror suspects, as the case of the so-called Times Square Bomber demonstrates. After Faisal Shahzad had been brought in, he was fed and advised of his Miranda rights. “He talked calmly and at length, for days, revealing key details about his plans and intentions.”

But in another case, in which torture was used, including waterboarding, sleep deprivation, and being shut in a tiny box, it turns out the useful information was given BEFORE any torture took place. And in general anything derived from mistreatment turns out to be thoroughly unreliable.

Morality

Another good chapter concerns snitches, and the “moral quicksand” around dealing with culpable co-operators. Surprise to say, it’s not all Goodfellas.

“The criminal justice system in any society necessarily implies a moral code. Law and morality are not coextensive, but to a significant degree what a society chooses to punish is a proxy for what it deems unacceptable, reprehensible, or immoral. Moreover, the way that a society chooses to enforce its laws, the practices it sanctions, the powers it grants, the tools it approves, also reveals the community’s moral thinking. In the risk gray zone of co-operators, that is especially true.”

“Flipping” a co-operator is a lot like obtaining a confession. You need to do your homework and earn their trust. When you do, the results can be devastating.

Justice

The human factor is critical. “In the end, the law doesn’t do justice. People do.”

It is troubling, though, how dependent justice appears to be on the right people being there are the right time. The system is fallible, not least because the people in it are fallible. The existence of innocence projects, and the huge numbers of cases brought to their attention, touched on here, bears testimony to the fallibility of the system. It is then left to heroic interveners to save who they may. It’s great when that happens, but it’s a bit of a lottery. It would be even better if the cases had been investigated and prosecuted with the patience and independence of mind that Bharara teaches. One can only hope that others coming up through the ranks will heed the good advice and learn from the lessons in this book.

“The road to justice is not always easy or even pure. Along the way there are distractions and detours, trade offs and Hobson’s choices. … It is not surprising, then, that it takes steel and nerve and delicate judgment to navigate that road.”

Doing Justice : A Prosecutor’s Thoughts on Crime, Punishment and the Rule of Law, by Preet Bharara. (Bloomsbury, £20)