Three Incan mummies sacrificed 500 years ago were drugged and given alcohol to make them more submissive, before they were left on top of a 22,000ft volcano in Argentina to freeze to death as part of a human sacrifice, researchers have found.

The three Inca mummies included a 13-year-old known as the Llullaillaco Maiden," a boy "Llullaillaco Boy," and girl "Lightning Girl" whose remains were struck by lightning and charred. The youngest appeared to be either 4 or 5 years old. The mummified remains were entombed in a small chamber 1.5 meters underground near the summit of Volcán Llullaillaco in Argentina.

Their well preserved remains were discovered in 1999 and have been on display in museums since then. The children were believed to have been participants in capacocha, a sacrificial rite that occurred in celebration of key events in the life of the Inca emperor.

For their latest study, researchers analyzed hair samples from the children which offers an unprecedented glimpse into their last moments before dying - possibly from hypothermia - and raise questions about the extent to which they knew of their impending fate as sacrificial objects.

"They look very recognizable as individuals, which adds to the poignancy of their story," says Andrew Wilson at the University of Bradford in the UK. "She has fantastically tightly braided hair, which effectively acts as a timeline stretching back almost two years before her death. Their human remains are the most well preserved mummies in the world, with blood still visible in their hearts and their lungs are still inflated.

Wilson and colleagues analyzed chemical traces in the hair differ from root to tip and learnt that she had a significant change in diet in her last two years of life. All three children consistently consumed coca leaves (from which cocaine is derived) and alcoholic beverages, while "Maiden" ingested a significant amount more than the others. The increase suggests drugs and alcohol to aid her compliance in a ceremony that culminated in her death.

Dr Wilson compared the team's findings with historical accounts produced by the Spanish, dating from the Colonial period, and said: "We think it's likely the maiden was selected for sacrifice 12 months before her death.

"She was then probably involved in a series of rituals, involving consumption of coca and alcohol, in the build-up to her sacrifice, which kept consumption at a steady level.

"Both substances were controlled, were considered elite products and held ritual significance for the Inca.

"At the altitude the children were found, death by exposure is inevitable. There was no evidence of physical violence to the children, but the coca and alcohol are likely to have hastened their deaths.

"The fact that in her final weeks the maiden shows consistently higher levels of coca and alcohol use compared to the younger children, suggests there was a greater need to sedate her in the final weeks of life."

The analysis was published Monday in the journal Proceedings of the National Academy of Sciences.

A study published in PloS ONE showed that the Maiden was suffering from a lung infection at the time of the sacrifice.