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The evidence of a homicide presented in a courtroom—exacting, and weighted down with scientific terms—can sometimes trip up jurors. These peers of the accused are trying to envision an act of grisly violence, often committed in a fit of rage or madness. Jurors don’t get to hold the murder weapon, and they can only guess what the victim and perpetrator felt at the crucial moment of death.

But a British murder trial recently placed a 3-D-printed portion of the victim’s smashed skull right in the hands of the jury, as they considered the severity of a fatal beating, as reported recently in the Journal of Forensic Sciences.

“The fact that 3D prints can be handled directly without protective packaging allows the jury and the judge to examine the part and the three-dimensional relationship between the injuries most closely with the potential to better understand the testimony given by the pathologist,” writes the team, from the University of Warwick, and the West Midlands Police in Birmingham.

The murder trial involved two defendants, two weapons and multiple accounts of what had happened to the single victim.

A next-door neighbor called police after hearing a violent fight, and responding officers apprehended two other occupants of the house attempting to flee, according to the paper. The victim had severe head trauma, and later died while undergoing surgery. The two defendants, charged with murder, blamed each other for the death.

Two suspected murder weapons were found at the scene: a claw hammer and a large wrench.

The skull of the victim underwent micro-CT scanning shortly after death, using a Nikon Metrology device. That hyper-detailed imagery showed the complex fracture patterns in the bone—and multiple impacts, according to the account.

The micro-CT data was then converted to surface mesh using a software program called Simpleware ScanIP, made by the California-based Synopsys, and then 3-D printed using a Formlabs Form2 printer, they report.

Two different fracture shapes emerged from the wounds: an elongated depression fracture, and one smaller square shape with rounded corners, they add.

The Crown Prosecution Service decided the 3-D print of the portion of the skull would be useful at trial. The benefits of using it included: the copy of the biological material did not pose health hazards by jury handling, and original evidence would not potentially be compromised by passing it around the courtroom. The victim’s family would also not be emotionally impacted by passing around a part of their loved one’s remains, according to the case study.

But a balance was necessary, so a jury wouldn’t be prejudiced by the visceral representation of deadly injuries. Prosecutors settled on using just enough of the cranium to get their point across, without making it too lifelike, they add. A small section of the skull with the fractures was made out of white resin—but was otherwise plastic in appearance and feel.

“This fine balance between realism and ‘sanitizing’ was struck in this case as the model was admitted without objections from either party,” they add.

The tangible feel for the injuries—and the crime—were thus given to the jury, who seemed to alertly respond when it was presented in the courtroom, the academics and the police authors recount in their paper.

“Upon observation, the jury in this case appeared interested and attentive, taking extensive notes, during the presentation of the 3-D print, a major benefit of demonstrative exhibits in general,” they write.

Both defendants were found guilty of the murder—and both received life imprisonment. The authors conclude that they cannot be sure of the effect the 3-D skull fragment played in the jury’s decision.

Murder cases have relied on the 3-D printing of skulls, as well as other vital evidence, like weapons.

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