These were the first detectives

From Murder in the First-Class Carriage: The First Victorian Railway Killing by Kate Colquhoun. Page 26.

Thomas Briggs’ death [in 1864] meant that, for the first time since the invention of the railway, a murder had occurred on a British train. As the news reached his office across London at 4 Whitehall Place, the Police Commissioner Sir Richard Mayne recognised that his force would be expected to move swiftly and decisively or face the public’s wrath. He believed that he had just the man for the job.

In 1842 – only thirteen years after the establishment of the first five divisions of the Metropolitan Police by Sir Robert Peel – Mayne and his co-chief Charles Rowan had obtained government sanction to create a new species of police inspector. No longer primarily concerned with the prevention of crime and without the visible authority of a uniform, these were the first detectives: eight conscientious men were selected, including Stephen Thornton and Jack Whicher. Encouraged by the adulation of writers like Dickens, Britain had broadly allowed itself to be seduced into a belief in the brilliance of these perspicacious, dogged, plain-clothed detectives. Scepticism, though, was growing, and admiration was balanced by distrust as delays and irresolution from the elite investigators emphasised their fallibility. With this railway murder to solve, their reputation, once again, was on the line.

The first railroad was in 1825. 39 years was a pretty good run.