Exhibit B

When I was nine, my mother brought home something remarkable. A young woman, I think a graduate student in my father’s lab, followed her into our bathroom. Soon the smell of formaldehyde wafted into the living room. The next day, my mother, wearing a denim button-down shirt with embroidered Looney Tunes characters over the breast pocket, visited my grade 3 class. During her presentation, she passed around a pickled rat brain that resembled a beige rubber walnut. A large glass vessel held the human brain that she had decanted and transferred into fresh preserving solution over our bathtub the night before.

My dad is a neuroscientist, and my mom is an expert in pediatric motor-speech disorders. When I was a child, they enrolled me in studies where friendly researchers asked me to arrange plastic blocks into shapes or to hold still as I disappeared into the whirring barrel of an fMRI machine. To reach my father’s office — in the sub-basement below a statue of Wilder Penfield, the groundbreaking neurosurgeon — we would cut through the pathology department and walk down a hallway decorated with historical specimens floating in yellow liquid. I was warned not to go through any of the swinging doors. Behind them, I grasped vaguely, might be corpses.

Twenty years later, I found myself in the Public Record Office Victoria, in Melbourne, with a hard drive filled with images of prison ­registers, trial transcripts, coroner’s reports, ­asylum casebooks, and council minutes. I was midway through my doctoral research on criminal responsibility in the British Empire, which would also take me to archives in Canada, England, and the United States. By now, my childhood interest in brains had been filtered through training in law and history. The smell of the fine dust that puffs from the spines of old leather volumes had replaced that of formaldehyde, as I worked through nineteenth-century capital case files compiled by long-ago government agents.

Crimes in which the accused’s mental state was in doubt pushed officials to articulate their assumptions about the minds and moral fibre of British subjects. How much forbearance or intelligence was it fair to expect, especially in the distant corners of a sprawling empire? What degree or kind of insanity — perhaps even just mental weakness or “barbarism”— should spare a killer the noose? What did such questions mean for the fantasy of imperial rule through law? As they do today, experts took the stand, often revealing in their testimony the uncertainties and factionalism that beset forensic psychiatry — then a branch of “medical jurisprudence.”

The rapidly developing field of mental ­science intersected with Victorian theories about sex, race, and civilization; increasingly expansive definitions of mental deficiency reflected the pessimism of the age and the ambition of physicians and imperialists alike. But was British criminal law fit to govern an unfit empire? Case files capture these nuances in black and white — and, as I discovered, red.

While elderly genealogists across the table from me pored over birth records, I unfolded a crumpled scrap I had carefully extracted from an envelope marked “Exhibit B.” The case was that of William Colston, who had killed a neighbour and his wife with an axe and fled. His defence hinged on a claim that he was insane. The jury voted to convict, and Colston was hanged at Melbourne Gaol in 1891. “Exhibit B,” it turned out, actually contained two pieces of paper that fit together like parts of a jigsaw puzzle. Each was marked with half of a rust-brown blood stain — one had been found on Colston, the other at the scene — that proved he was the killer.

Archival documents often hint at the rich ordinary lives of people in the past; they can generate a peculiar intimacy between researcher and subject. So writing biographically informed, narrative histories can feel like breaking a confidence. Running my fingers over that dried blood brought me even closer to William Colston — and not just to his mind. It was like standing outside a bathroom with a disembodied brain inside it: a visceral reminder that the body is a physical thing and that its parts can make strange journeys long after death.