Scientists initially presumed that the Stone Age Iceman, nicknamed Otzi, was caught in a storm and froze to death. But a new team said Monday that Otzi's case instead has become the world's oldest, and coldest, murder case.

"We've been working round the clock for the last three weeks to get these results," DNA specialist Thomas Loy of the University of Queensland in Brisbane, Australia, told USA TODAY Monday by phone from a laboratory in Bolanzo, Italy. "It was very exciting when the blood samples came back positive for human DNA from four separate individuals."

Otzi's naturally mummified body, the oldest found so far, became a worldwide sensation in 1991 after two Austrian mountain climbers saw it in a thawing glacier at 10,500 feet on the Hauslabjoch Alpine pass at the Italian/Austria border. Nearby artifacts included a copper blade ax, a bearskin cap, shoes of bearskin and woven grass, a quiver of arrows, and a knife

In 2001, an Italian radiologist found an arrowhead embedded in Otzi's shoulder. Otzi had been hit from behind and managed to pull out only the shaft. That discovery led Eduard Egarter, Bolanzo's chief medical examiner and curator of Otzi's body, to look for more evidence of a fight.

Alois Pirpamer, one of the climbers who found Otzi, told Egarter that the Iceman had been clutching a knife in his right hand at the time of the discovery. The knife came loose when the body was pulled from the ice. Pirpamer says he told the Austrian scientists that Otzi was holding the knife, but was ignored.

Egarter matched the knife to the hand and found a deep gash on the hand that had been missed in previous studies. He then found another cut on the left hand and bruises on the torso, as if Otzi had been beaten. Documentary filmmaker Brando Quilici, who was making a second film for the Discovery Channel on the Iceman, suggested bringing in Loy to look for microscopic blood samples that might belong to the attackers. Blood from one person was found on the back of Otzi's cloak, and blood from two people was found on the same arrow in his quiver. More blood was on the knife.

Quilici says the team suspects blood on the back of the cloak may have come from a wounded colleague that Otzi was carrying over his shoulder. Loy says blood of two people was found on the same arrow, suggesting Otzi killed both men and retrieved the arrow.

With Europe gripped in a heat wave, Quilici says ice at the Alpine pass is melting fast. The team will look for more bodies there on Aug. 28.