The murder case has been open now for two and a half millennia, and scientists suspect they've found a clue that could unlock the missing details.

Ötzi, the impeccably preserved mummy found in the Alps one day in 1991, has been under the careful watch of researchers and scientists. So far they've already reconstructed his face, diet, clothing, entire genome, and now, the surrounding details of his potential murder.

While he also reportedly suffered from heart disease, joint pain, tooth decay, and Lyme disease, the arrow wound in Ötzi's shoulder is the smoking gun for researchers, as the wound penetrates deep into an artery. The food in his stomach was also undigested, an indication Ötzi was ambushed soon after eating.

A few years ago, a CT scan showed dark spots on the back of Ötzi's cerebrum, which scientists suggested may have shown up from the brain bashing into the skull — indications of a blow to the head.

Using the proteins found in his brain tissue, scientists have now proven the bruising conclusively, citing the clotted cells in the corpse's brain as indications of bruising. Whether this blunt force trauma occurred as a direct result of an attacker, or from the attack's resulting fall, is still unclear.

Out of the 502 proteins scientists observed, 10, they said, were related to blood and coagulation. The sample also revealed proteins related to stress response and wound healing.

Proteins are useful for researchers because they provide a unique biological timestamp, in ways that DNA cannot.

"Proteins are the decisive players in tissues and cells," Andreas Tholey, scientist at Germany's Kiel University and a researcher on the new Ötzi study, said in a statement. "And they conduct most of the processes which take place in cells."

If the body's various proteins were represented by a person's age, address, phone number, and credit card number — transient indicators of identity over the course of a life — DNA would be the social security number.

"Identification of the proteins is therefore key to understanding the functional potential of a particular tissue," Tholey added. "DNA is always constant, regardless of from where it originates in the body, whereas proteins provide precise information about what is happening in specific regions within the body."

The studying of mummified tissue often proves fickle and frustrating for scientists. For these reasons, Ötzi's case has scientists particularly intrigued and excited.

"Investigating mummified tissue can be very frustrating," study author and microbiologist Frank Maixner, of the European Academy of Bolzano/Bozen (EURAC), said in a statement. "The samples are often damaged or contaminated and do not necessarily yield results, even after several attempts and using a variety of investigative methods."

So the case isn't closed. But scientists are moving toward uncovering greater truths about how the body stays preserved over time, and what clues are latent in that preservation.

"When you think that we have succeeded in identifying actual tissue changes in a human who lived over 5,000 years ago," he continued, "you can begin to understand how pleased we are as scientists that we persisted with our research after many unsuccessful attempts."