The rain has been coming down for hours and the heavy clay soil under my feet is quickly turning into a quagmire. I am on a mountainside in the highlands of Guatemala, a three-hour drive and gruelling four-hour walk away from the small rural town of Nebaj, El Quiche, in a region known as the Ixil Triangle. The rain has soaked through my clothes and my fingers are so numb that I can barely feel the trowel in my hands, but I continue to work, anxious not to miss any of the evidence that the grave in front of me holds.

I pick up a skull and begin to gently rub away some of the dirt. This young man was executed with a single gunshot to the back of the head, a common form of execution in this area strewn with clandestine graves. I begin to lift the ribcage where I find signs of another impact wound; he was shot twice from behind. A quick check of the rest of the skeleton gives me an idea of his age at death: less than 21. Next to him lies the skeleton of his father. What must their last thoughts have been before the bullets struck?

I glance up. The woman beside me is peering into the grave, watching my every move with a look not of despair or fear but of strength and courage. She is their wife and mother, the only member of her family to survive the horrors that were inflicted upon so many some 25 years ago. The sky blackens and the rain seems to pick up a rhythm¡­

This passage may sound something like an extract from a crime novel, but in fact it describes one of the many hours I spent exhuming graves when I worked for the Guatemalan Forensic Anthropology Foundation. The graves hold the bones of a story, one that is grounded in the shocking fact of modern Guatemalan history. That story begins in the 1960s, when the military successively infiltrated and took control of the government. A peasant movement began to demand land reform but during the 1980s a series of military dictatorships - supported by the tiny minority of excessively wealthy landowners - brutally suppressed the uprising. During this period, small groups of indigenous farmers took up arms, supported by the political Left, the intellectual community and the Catholic Church.

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The uprising began in the most impoverished areas. As these were also the indigenous regions, the military government quickly used this as an excuse to attempt an annihilation of the Mayan people. Much of the population suffered appalling abuses: the killings were not limited to men of fighting age. Attacks were indiscriminate. In a policy known as ¡°scorched earth¡±, whole villages were burnt as sympathisers of the guerrilla army were sought. During the six years I spent working for the foundation, I exhumed the corpses of babies, children, pregnant women and the old and infirm, all innocent victims caught up in the conflict. Military camps were filled with detainees, who were often tortured then executed and thrown into mass graves. It was only many years later, in the early 1990s, that those graves began to be exhumed and Guatemala finally confronted the horror of its past. The Guatemalan mountainsides remain littered with secrets - secrets only the dead, and those trained to reveal them, can give up.

How, you may ask, does a secondary school geography teacher end up working as a forensic anthropologist in one of the most violent countries in the world? Well, I have always been drawn to detective fiction and the need to get to the truth, and I was fascinated by forensic science. At the same time, I loved Latin American culture. These two interests combined after I learned, with utter disgust and disbelief, about the plight of Guatemalan refugees when I was teaching English in Southern Mexico. My fate was sealed. Equipped with an undergraduate degree in geography, I somehow managed to convince the coordinator of University College London¡¯s master¡¯s programme in forensic archaeological science of my unwavering determination to work in Guatemala as a forensic anthropologist. So I left Mexico, took some archaeology courses over the English summer and began my UCL studies in September 2003. In October 2004, armed with a distinction in forensic archaeological science, I naively thought I knew enough to help. Before I knew it, I was on a bus to Guatemala City (well, several so-called ¡°chicken buses¡±, in fact: old American school buses painted in garish colours form the backbone of the transport network in Guatemala, transporting anything from huge sacks of corn to chickens and people crammed in tightly, hence their name), commuting from my home in Mexico each week.

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I still remember arriving at the house where the foundation has its laboratories and offices. A huge rambling affair, it was surrounded by whitewashed walls and topped with barbed wire - a feature that is not unusual in Guatemala City. The only indication that this was not a typical residence was the police guard on the gate: the foundation has been receiving anonymous death threats since its founding in 1992 and it remains prudent to have someone keep a lookout for any unusual activity.

I was instantly put to work assisting in the analysis of hundreds of skeletons recently exhumed from the towns and villages around Guatemala. Right away, I knew that I had made the right choice. This is what I wanted to do: help people to find their family members who had been so tragically taken from them. Around 20 tables in the lab held remains. Families would often visit and Mayan rituals were performed, with candles lit, flowers laid and tears shed. But this painful scene represented the beginning of closure. Many of the victims had disappeared 25 years earlier and had never been seen again. For those left behind, the agony of not knowing was greater than the pain of knowing. For this reason, as strange as it may seem, returning the remains to their families was a time of celebration as well as sadness. Preparing detailed forensic reports for the prosecutor¡¯s office, with the almost futile hope of bringing the murderers to justice one day, was another cornerstone of the foundation¡¯s work.

It was with more than a hint of sadness that I left Guatemala two years ago to take up a lecturing post at the University of Lincoln. But with two young children and the violence in the country seeming to increase on a daily basis, I felt it was time to hang up my trowel. These days I share my knowledge and experience; I aim to inspire a new generation who will be equipped to go out into the world and investigate the human rights atrocities that continue to occur. Sadly, the news is always full of countries in which despotic leaders commit horrendous abuses in their desperation to cling to power. The move back to the UK also opened new doors: I recently found myself in Kabul, Afghanistan, consulting for Physicians for Human Rights, an international organisation, training a team of Afghans to carry out mass grave investigations. Afghanistan, like Guatemala, has a lot of bloody history to reconcile.

I am also lucky enough to have been invited to give talks about my work around the UK. I suppose this is my small personal tribute to the victims of Guatemala: unashamedly, I see it as a vehicle for raising awareness about the injustice suffered by a small population living on the other side of the globe. But sometimes I do find it difficult to explain to people what I did in Guatemala and what I do today; their reactions range from macabre fascination to bewilderment. Wherever I go, I am usually asked the same question: how do you cope emotionally with the work, seeing all the grief and destruction of family life first-hand? The truth is that when dealing with the most horrific cases of torture and mass murder of innocent people, it is impossible not to be overcome by a deep sense of loss and helplessness sometimes. I am always conscious, however, that this is what I trained to do and that I have a duty to carry out the best possible work I can. You learn to control your emotions because it is hard to perform to a high scientific standard if you cannot get past that - it begins to affect your judgement.

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Many memories from Guatemala will stay with me for ever: the two sisters killed by a single bullet as they ran away from the soldiers, the elder sister carrying the younger on her back; the mother who lost her legs in an aerial bombing of her village and who is condemned to sit inside her small house unable to move. But one of my lasting memories is of a group of women hugging me and thanking me for walking to their remote village. I was on a preliminary visit to an exhumation. ¡°I haven¡¯t done anything,¡± I mumbled in embarrassment. ¡°Oh, but you have,¡± one woman said. ¡°You have come all the way from Europe to listen to our story and we can¡¯t thank you enough.¡± In my view, though, it is those who are brave enough to stand up to injustice in the face of such adversity who really deserve our thanks.