The iceman was discovered by German tourists
It was thought the man died from cold and hunger. But researchers now say they have discovered an arrowhead in the man's left shoulder.
They speculate that Oetzi may have fled his attacker before bleeding to death and being entombed in ice.
Shrunken and shrivelled
The iceman was discovered by German tourists in 1991 in the Oetz Valley - hence the name - still wearing goatskin leggings and a grass cape. His copper-headed axe and a quiver full of arrows were lying nearby.
The corpse had been shrunken and shrivelled by the effects of time and cold, but was otherwise remarkably well preserved.
Scientists were extremely cautious about damaging the body as they tried to learn from it - particularly as the mummy was also the subject of a political dispute, having been found just metres inside Italy, but initially taken away by the Austrian authorities.
Oetzi's permanent home is now at the South Tyrol Museum of Archaeology in Bolzano, Italy.
Painful death
A radiologist in the investigation team, Paul Gostner, said a two-centimetre-long stone arrowhead had been found in Oetzi's left shoulder.
Eduard Egarter Vigl, another of the researchers, said the arrow shattered the scapula, tearing through nerves and major blood vessels and paralysing the left arm in what must have been an extremely painful death. It probably took 3 to 10 hours for him to die, he said.
It is possible, the researchers say, that Oetzi may have fled from his attacker to the spot where he was entombed in the ice.
Scientists at the museum are hugely excited by the discovery. The museum's director, Alex Susanna, said it disproved all other theories about Oetzi's death:
Ancient society
"All the things that have been published over the past seven or eight years - that he died because of broken ribs, that he died under the snow, or that he was exhausted and laid down and fell asleep and froze to death - are wrong," she said.
"Maybe there was a combat, maybe he was in a battle. There is a whole series of new implications. The story needs to be rewritten."
Scientists hope to use the new information to reconstruct the last hours of the iceman's life and his role in ancient society.
Previous investigation has already shown that the Iceman was between 45 and 50 years old when he died, which was very old for that era - around the time when humans were switching from using stone to metal tools.