In 2010, the body of 13-year-old Yara Gambirasio was found in a snowy field not far from her home in a small Italian town.
She was covered in dozens of superficial knife lacerations, but it is believed she froze to death while unconscious.
DNA samples recovered at the scene pointed police to a suspect who became known as “Ignoto Uno,” the Unknown One...
...and it would take nearly two years for investigators to link the genetic profile to a local man, Giuseppe Guerinoni.
Closely matching DNA was obtained from the back of a stamp found on a letter in a box of Guerinoni’s documents...
...but complicating matters was the fact that Guerinoni had been dead since 1999 – 11 years prior to the murder.
Guerinoni had three daughters with his widowed wife who were all quickly ruled out as suspects due to the nature of the crime...
...leading police to believe that he had at least one secret son who was born of an affair and who was not known to his family.
Investigators tracked down 532 women who Guerinoni potentially knew during his lifetime and created genetic profiles...
...hitting a match with Ester Arzuffi, who had been married her entire adult life and only had three children with her husband.
Both were shocked to discover, however, that their older twins had actually been fathered by Guerinoni during a brief tryst...
...and a DNA sample was obtained from the male twin, Massimo Bossetti, by breathalyzing him at a fake DUI checkpoint.
Even though Bossetti’s DNA was a near perfect match to the killer, he maintained his innocence until his 2016 conviction...
...after it emerged that he had been deeply concerned if his mother knew Guerinoni when police were looking for his mysterious son...
In early 1990, three separate female hitchhikers were found nude and shot dead near the Spokane River in Washington.
All were victims of the same .22-caliber handgun, leading police to believe the deaths were the work of a serial killer.
Lacking any other substantial evidence, the cases went cold until the infamous 2000 arrest of Robert Lee Yates...
...a local “family man” who confessed to the murders of 13 women and was later found to have omitted at least three more.
Investigators suspected that the 1990 murders were earlier crimes that Yates had simply forgotten...
...but new DNA testing in 2009 revealed the deaths were unrelated to Yates and pointed to a new unknown male perpetrator.
The genetic profile initially failed to match any potential male suspects in a DNA database of convicted offenders...
...but a more extensive search in 2012 turned up a hit on a female, Donna Perry, who was already in custody on weapons charges.
Digging into her case file, it was discovered that the woman had been “Douglas Perry” prior to gender surgery in 2000...
...and that during her unrelated arrest, detectives found a room painted shut in her house filled with women’s undergarments.
When the evidence was reexamined, the belongings were linked to the 1990 victims, apparently having been kept as trophies.
In her defense, Donna Perry claimed that she suffered from gender psychosis and that “Doug” was the real killer...
Another mysterious death was only recently illuminated by a study in the American Journal of Forensic Medicine and Pathology...
...after investigators described finding the body of an unidentified man in his cottage in a bizarre and “grisly” state.
The man had been renovating his cottage alone, and police were called to check on him after he stopped answering his phone.
First responders were completely confounded when they arrived, as it appeared that the man had spontaneously combusted.
70% of his body was covered in burns, yet there was no soot in his airway and he showed signs of heart failure.
The cottage interior also showed no evidence of a fire and there were no indications of any sort of electrical malfunctions.
Forensic scientists only put the story together when they recalled thunderstorms passing through at the man’s time of death...
...and an examination of the scene revealed that the cottage had steel beams near where the man had died between metal sawhorses.
The study in the journal concluded that the deceased was likely electrocuted when the cottage was struck by lighting...
...sending electricity down the beams and creating a secondary indoor arc of lightning between the work benches and through him...
In 1995, it was first noticed that over 100 children a year seemed to be suffering eerily similar deaths in Bihar, India...
...thought to be caused by a mystery disease that always struck in the middle of the night during the early months of summer.
It was reported that the afflicted children would awake screaming in the dark before seizing and losing consciousness...
...symptoms that were typically followed by severe swelling of the brain and eventual death in nearly half of all cases.
The regular annual outbreaks baffled doctors and scientists for over two decades as they struggled to identify a trigger.
Victims showed no sign of infection or immune response, but instead often suffered from dangerously low blood glucose levels.
It would not be until 2015 that CDC researchers were able to develop a genetic test to examine the blood sugar abnormality...
...eventually discovering metabolic imbalances that implicated a glucose-inhibiting organic compound, hypoglycin.
Further analysis revealed that the toxin was found in the lychees harvested every year around time of the unexplained deaths.
Scientists believe the children were eating lychees on an empty stomach and have now issued a warning about the fruit’s dangers...
In 1959, a group of nine hikers died under creepy and unexplained circumstances while trekking in Russia’s Dyatlov Pass...
...showing signs of hypothermia and physical trauma after having fled their campsite in the middle of the night.
Investigators concluded that an "unknown compelling force" had caused the deaths and closed off access to the area...
...generating rumors of secret military weapons tests, UFO activity, or a deadly encounter with a cryptozoological monster.
The case remained unsolved until a 2013 study attempted to offer a scientific explanation of mysterious event...
...hypothesizing that infrasound waves may naturally occur in the pass and may have driven the hikers into a fatal panic attack.
It is theorized that wind channeled around Holatchahl Mountain could create a phenomenon called a “Kármán vortex street”...
...a repeating pattern of swirling vortices that can generate an ominous hum at a frequency unsettling to humans.
Such a sound may have driven the hikers mad or convinced them that an avalanche was traveling down the mountain towards them.
Forensic analysis of their tent showed that it had been cut from the inside, giving credence to the idea they fled in confusion...