How were murder investigations conducted in the Middle Ages?

So I’m going to talk about an exceptional case, because it’s spectacular.

It’s 1407. The queen of France was down in the dumps after losing her newborn son in childbirth. Louis, unpopular duke d’Orleans and manipulative brother to King Charles—and rumored to be the baby’s father, just one of his many sexual dalliances—had just paid the grieving queen a visit to console her. After their evening meal together, a messenger appeared: the king had urgent business for Louis. Accompanied by two squires and four valets, the duke hoisted himself onto his mule and set off into the dark streets of Paris. They turned down the Rue Vielle du Temple, the duke “humming a tune” in good spirits. Upstairs in one tenant house, Jacquette Griffard was folding her baby’s diapers and watching out the window for her husband to come home. She paid little attention to the house across the street, which had stood empty for the past six months.

As Louis and his party drew even with the houses, the gates of the abandoned hotel burst open and a band of masked men suddenly swarmed the street in front of Louis. They carried torches. They carried axes and swords and maces studded with iron spikes. And they shouted, “It’s him. Kill him! Kill him!”

They fell upon the duke. The squires and two valets managed to flee. Two valets bravely sought to defend their duke, one dying for his valor and the other escaping, grievously wounded. The desecrated, mutilated bodies of Louis and Jacob de la Merre lay in the Paris street.

And the abandoned hotel was on fire.

Fire was a massive threat in any medieval or early modern city. Worried neighbors appeared in the street to investigate, and the cry of “Murder” went up.

The king charged Guillame de Tignonville, provost of Paris, with the pursuit of the perpetrators, affording him whatever manpower and powers he needed.

Tignonville did two things immediately. First, he ordered the gates of Paris shut, so the murderers would be trapped in the walled city. Second, he inspected the body. This was the necessary first step of any murder investigation: to ascertain that a murder had in fact been committed. In Tignonville’s meticulous notes of the case (reflecting its importance—the prince of France was dead), we see the language of investigatorial skepticism already: “The street where the crime is said to have been committed” and “it appeared that the wounds caused their deaths.” (“…And the wounds were of such a kind,” he writes, “that the head was all sliced up and the entire brain protruded.”)

The provost’s investigation itself followed two familiar paths: interviews of witnesses and examination of physical evidence. His army of clerics went door-to-door in the apartments and shops on the street. If someone admitted any knowledge, they were interviewed further with a scribe to record their words. In the abandoned hotel, he found various items left behind by the masked murderers. With those objects, he went from shop to shop in Paris, asking if the shopkeeper had sold them, and to whom. Witnesses misremembered and lied; evidence didn’t pan out; Tignonville grew frustrated but perservered. Louis had had so many enemies, in low places and high; the list of suspects was endless.

Finally, he tracked down two key witnesses: the man who had arranged for the gang to occupy the house, and shopkeepers who recognized items they had sold. The problem: the conspirators behind the crime were as high placed as the royal family itself, and in the Middle Ages, obtaining a confession (by any means necessary) was essential.

So Guillame devised a trap.

It was not normally allowed, he admitted to the royal council, for an investigator to search the palaces of high lords. But surely they would be willing to submit to one, if they had nothing to hide...

And one of the dukes--a member of the royal family, even--confessed immediately. Tignonville never even had to search his residence for evidence (or rather "evidence"). Simply the idea that he might find something was enough to draw out the culprit. True to form for any modern crime drama, he had been spotted at Louis' funeral loudly proclaiming that never before had a more treacherous murder been committed in the streets of Paris.

My source on this is Eric Jager's fantastic Blood Royal: A True Tale of Crime and Detection in Medieval Paris, which I hope you will consider obtaining through your local or university library (a sentiment which I hope does not count as advertising).