Daniel M’Naghten was found not guilty of murder in 1843 because the medical witnesses at his Old Bailey trial convinced the jury that severe paranoid delusions had left him unable to understand that shooting Edward Drummond was wrong. The testimony was so one-sided that the jury acquitted on the ground of insanity without leaving the box. In their finding, M’Naghten genuinely believed he was defending himself against a conspiracy that wanted him dead, and that belief was the product of a diseased mind rather than criminal intent.
The Shooting on a London Street
On January 20, 1843, M’Naghten walked up behind Edward Drummond on a London street and shot him in the back with a pistol. Drummond was the private secretary to Prime Minister Sir Robert Peel, and M’Naghten almost certainly mistook him for Peel himself. Drummond died from the wound days later.1Old Bailey Online. Daniel M’Naughten, Killing, Murder, 27th February 1843
The intended target matters, because the reason M’Naghten wanted Peel dead was the same reason his lawyers argued he should not be convicted.
The Delusions That Drove the Attack
M’Naghten was the son of a Glasgow woodturner and had been suffering from paranoid delusions for years before the shooting. He was convinced that a conspiracy of Tories and Catholic priests was spying on him, following him from city to city, and plotting to kill him. This was not a passing suspicion. Roughly two years before the shooting he had contacted the Commissioner of Police begging for the persecution to stop, and later reminded the Commissioner again. When no relief came, he apparently decided to strike at the person he believed was behind it all: the Prime Minister.
In his own mind, he was not committing murder. He was defending his life against an enemy who would otherwise kill him first.
The Defense Theory
M’Naghten was tried at the Old Bailey on February 27, 1843. His defense was led by Alexander Cockburn, who built an unusually sophisticated case around the idea that delusions caused by mental disease could destroy a person’s ability to tell right from wrong. Cockburn drew heavily on Isaac Ray’s Treatise on the Medical Jurisprudence of Insanity, an American work that rejected the older view that a defendant had to be completely deranged to qualify as insane. Ray argued that mental illness could distort specific areas of reasoning while leaving others intact.
The shift mattered. Before M’Naghten’s trial, English courts generally required something close to total madness before excusing a defendant. A person who could hold a conversation, dress himself, and manage daily tasks was often presumed sane enough to be convicted. Cockburn argued that M’Naghten could do all of those things and still lack the capacity to understand that killing Drummond was wrong, because his paranoid delusions were so powerful they overrode his moral reasoning on that specific subject.
The Medical Testimony That Convinced the Jury
Several physicians and specialists testified that M’Naghten suffered from what they called monomania: an intense fixation on a single delusional belief that dominated his thinking despite apparent rationality in other areas. They described his conviction that enemies were constantly pursuing him as genuine, deeply held, and impossible for him to shake through reasoning or evidence.2Legal Information Institute. M’Naghten Rule
The witnesses were emphatic that the delusions were not an act. M’Naghten had exhibited these beliefs consistently for years, to multiple people, in circumstances where faking would have served no purpose. Their testimony painted a picture of a man whose perception of reality was so distorted that he believed he was acting in self-defense when he pulled the trigger. The killing, in his mind, was justified because the alternative was his own murder at the hands of the conspiracy.
The medical evidence was so uniform and so unchallenged that the prosecution effectively had nothing left to argue. The jury returned a verdict of not guilty on the ground of insanity without even retiring to deliberate. The core finding was straightforward: M’Naghten’s disease of the mind produced delusions so severe that he did not understand the wrongfulness of what he was doing when he shot Drummond.3Justia. M’Naghten’s Case
What Acquittal Actually Meant for M’Naghten
The verdict did not mean M’Naghten walked free. He was committed to Bethlem Royal Hospital, the institution commonly known as “Bedlam,” where he remained for roughly twenty years. In 1864 he was transferred to Broadmoor Asylum, and he died there on May 3, 1865, at the age of 52. He never regained his freedom. His acquittal spared him execution and replaced it with indefinite confinement in a psychiatric institution.
The Rules His Acquittal Produced
The public reaction to the verdict was intense. To many people, the idea that someone could shoot a man in broad daylight and avoid a murder conviction felt like a failure of the legal system. Queen Victoria herself wrote to Peel on March 12, 1843, expressing frustration that whenever the insanity law was tested, it seemed “of no avail.” Her concern added political pressure to an already heated debate.
The House of Lords took the unusual step of summoning the judges of the Court of Common Pleas to answer a series of abstract legal questions about when insanity should excuse a crime. The judges’ answers, delivered in response to five questions about what juries should be told when insanity is raised as a defense, became the foundation of a new legal standard.3Justia. M’Naghten’s Case
Those answers crystallized into the M’Naghten Rules. Every defendant is presumed sane. To succeed with an insanity defense, the defendant must show that at the time of the act, a disease of the mind caused such a breakdown in reasoning that either they did not understand the nature of the act they were performing, or they did not know that what they were doing was wrong.2Legal Information Institute. M’Naghten Rule
M’Naghten himself fell into the second category. He knew he was firing a pistol at a person. What his disease prevented him from grasping was that doing so was wrong, because his delusions told him the act was necessary self-defense.
There is an irony worth noting. The rules born from M’Naghten’s acquittal were actually stricter than the standard applied at his trial. Cockburn’s defense had argued a broader theory that included the idea that delusions could compel behavior the defendant could not resist. The M’Naghten Rules deliberately rejected that volitional element and focused exclusively on what the defendant knew or understood. Under the test that bears his name, a future defendant in M’Naghten’s position would still qualify, but only because his delusions destroyed his understanding of wrongfulness, not because they compelled him to act.