The Murder of Meredith Kercher: What Did the DNA Evidence Really Prove?

On November 2, 2007, 21-year-old British exchange student Meredith Kercher was found murdered inside the apartment she shared with three other women in Perugia, Italy.

What followed became one of the most famous—and controversial—murder investigations in modern history.

Meredith’s American roommate, Amanda Knox, and Knox’s new boyfriend, Raffaele Sollecito, were arrested and eventually convicted of her murder. Their convictions were overturned, reinstated, and ultimately thrown out for good by Italy’s highest court in 2015.

At the center of that years-long legal battle was forensic evidence—particularly DNA.

But what did that DNA actually prove?

The Murder of Meredith Kercher

Meredith, known as “Mez” to her friends, had traveled from England to Italy as part of a study-abroad program. She was studying at the University of Perugia and had been living in the city for only a few months when she was killed.

On the evening of November 1, 2007, Meredith returned home after spending time with friends.

The following afternoon, her locked bedroom door was forced open.

Inside, Meredith was found dead beneath a duvet. She had suffered extensive injuries, including two wounds to her neck. Investigators also discovered a bloody palm print, bloody shoeprints, DNA evidence and other biological material throughout the room.

The crime scene contained an enormous amount of forensic evidence.

And much of it pointed toward one person.

The Forensic Evidence Against Rudy Guede

Investigators eventually identified the bloody palm print inside Meredith’s bedroom as belonging to 20-year-old Rudy Guede.

His DNA was also recovered from Meredith’s body and belongings, while bloody shoeprints linked to his shoes traveled from her bedroom into other areas of the apartment.

Guede admitted being inside the apartment that night but denied killing Meredith. He claimed another man attacked her while he was in the bathroom.

He was eventually convicted in connection with Meredith’s murder.

But Italian investigators remained convinced Guede had not acted alone.

Their case against Amanda Knox and Raffaele Sollecito would rely heavily on two much more controversial pieces of DNA evidence.

The “Double-DNA” Knife

Police searching Raffaele’s apartment seized a large kitchen knife that prosecutors later alleged was the murder weapon.

Amanda’s DNA was found on its handle.

On the surface, that sounded incredibly incriminating—especially after analysts reported finding a microscopic DNA profile attributed to Meredith on the blade.

Prosecutors began referring to it as the “double-DNA knife.”

But there were problems.

Amanda regularly spent time at Raffaele’s apartment and prepared food there, providing an innocent explanation for her DNA being on a kitchen utensil.

There was no visible blood on the knife, and chemical testing for blood was negative. The biological material attributed to Meredith was also so small that the original test consumed the entire sample, meaning the result couldn’t be independently reproduced.

Court-appointed experts later reviewed the testing and concluded that the profile attributed to Meredith was unreliable.

Additional testing of another portion of the knife also failed to find Meredith’s DNA.

The supposed murder weapon suddenly looked much less conclusive.

The Bra Clasp

Then there was the evidence against Raffaele.

During the original crime-scene examination, investigators photographed the clasp from Meredith’s bra lying on her bedroom floor.

But they didn’t collect it.

Instead, the clasp remained inside the murder room for approximately 46 days.

When investigators finally returned and recovered it, the clasp had moved several feet from its original location. Video from the collection also showed investigators handling it under conditions that would later raise serious questions about contamination.

Testing revealed a mixed DNA profile containing Meredith’s DNA, genetic markers attributed to Raffaele and indications of additional male contributors.

Prosecutors argued that the result placed Raffaele inside Meredith’s bedroom during the murder.

The defense argued that it could have arrived there through contamination or secondary transfer.

And that distinction became incredibly important.

DNA can potentially tell investigators whose biological material is present. It cannot automatically tell them when that material arrived, how it got there or what someone was doing when it was deposited.

Mixed DNA, Luminol and a Staged Burglary

Prosecutors also relied on mixed DNA recovered from the bathroom Amanda shared with Meredith, footprints revealed by luminol and a partial bloody footprint discovered on a bathmat.

But each came with its own limitations.

Finding Amanda’s DNA inside her own bathroom wasn’t unexpected. And although luminol can reveal traces of blood, it can react with other substances as well. Follow-up testing did not confirm blood in several of the luminol-revealed footprints.

Investigators also believed a broken window in another roommate’s bedroom had been staged to make the murder appear to be a burglary.

The defense disputed that interpretation.

Meanwhile, one forensic fact remained especially significant: despite the amount of blood and biological material inside Meredith’s bedroom, no reliable forensic evidence placed Amanda inside the room during the murder.

Aside from the disputed bra-clasp sample, the same was true for Raffaele.

Convicted, Acquitted and Convicted Again

Amanda Knox and Raffaele Sollecito were convicted in 2009.

In 2011, an appellate court overturned their murder convictions after independent experts raised serious concerns about the forensic evidence.

Italy’s highest court later ordered another trial, and the pair were convicted again in 2014.

Then, on March 27, 2015, Italy’s highest court definitively acquitted both Amanda and Raffaele of Meredith’s murder.

The court criticized serious problems with the investigation and found no reliable biological evidence connecting either of them to Meredith’s body or the room where she was killed.

What Did the DNA Really Prove?

The murder of Meredith Kercher is an extraordinary example of both the power and limitations of forensic DNA.

The evidence connected Rudy Guede directly to Meredith and the immediate crime scene.

The evidence involving Amanda and Raffaele was very different.

Amanda’s DNA on a kitchen knife from her boyfriend’s apartment demonstrated that she had likely handled it—but not why.

The microscopic trace attributed to Meredith on the blade could not be reliably confirmed.

And the bra clasp allegedly containing Raffaele’s DNA had remained unsecured inside the murder scene for 46 days before being collected under highly controversial conditions.

DNA evidence can sound absolute. Words such as “match,” “compatible” and “profile” can feel like scientific proof of guilt.

But DNA does not tell an entire story on its own.

Collection matters. Contamination matters. Location matters. And perhaps most importantly, context matters.

In this episode of Forensic Tales, we take a deep dive into the murder of Meredith Kercher and examine the knife, bra clasp, blood evidence, luminol footprints, disputed crime-scene processing and DNA evidence that helped fuel one of the most controversial murder prosecutions in modern history.

And throughout it all, we return to the person who too often became secondary to the spectacle surrounding her case.

Her name was Meredith Kercher.

She was 21 years old, deeply loved by her family and friends, and had traveled to Italy expecting the beginning of an incredible new chapter.

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