Image caption "The Iceman" has been the subject of constant study for more than 20 years

New clues have emerged in what could be described as the world's oldest murder case: that of Oetzi the "Iceman", whose 5,300-year-old body was discovered frozen in the Italian Alps in 1991.

Oetzi's full genome has now beenreported in Nature Communications.

It reveals that he had brown eyes, "O" blood type, was lactose intolerant, and was predisposed to heart disease.

They also show him to be the first documented case of infection by a Lyme disease bacterium.

Analysis of series of anomalies in the Iceman's DNA also revealed him to be more closely related to modern inhabitants of Corsica and Sardinia than to populations in the Alps, where he was unearthed.

'Really exciting'

The study reveals the fuller genetic picture as laid out in the nuclei of Oetzi's cells.

This nuclear DNA is both rarer and typically less well-preserved than the DNA within mitochondria, the cell's "power plants", which also contain DNA.

Image caption A reconstruction shows what Oetzi may have looked like before an arrow felled him

Oetzi's mitochondrial DNA had already revealed some hints of his origins when it was fully sequenced in 2008.

Albert Zink, from the Eurac Institute for Mummies and the Iceman in Bolzano, Italy, said the nuclear DNA study was a great leap forward in one of the most widely studied specimens in science.

"We've been studying the Iceman for 20 years. We know so many things about him - where he lived, how he died - but very little was known about his genetics, the genetic information he was carrying around," he told BBC News.

He was carrying around a "haplotype" that showed his ancestors most likely migrated from the Middle East as the practice of formal agriculture became more widespread.

It is probably this period of transition to an agrarian society that explains Oetzi's lactose intolerance.

Prof Zink said that next-generation "whole-genome" sequencing techniques made the analysis possible.

"Whole-genome sequencing allows you to sequence the whole DNA out of one sample; that wasn't possible before in the same way.

"This was really exciting and I think it's just the start for a longer study on this level. We still would like to learn more from this data - we've only just started to analyse it."