'My dad was a powerful man; physically robust,' says Bridges. 'He had been an amateur boxer when he was younger and I remember when I was a child he would bend a quarter [an American coin] in his fingers. I don't think there are too many people who are able to do that. He was immensely strong, even at 71. In his autopsy report, the doctor went on about how surprisingly physically well-built and strong he was for a man of that age.'

Campbell Bridges led a spartan existence. Although the family residence was a house built especially for them on a hilltop - which he named Leopard Hill, after the graceful animals who shared it with them - he preferred sleeping in a tree house nine metres above the ground.

'He didn't need many home comforts,' says Bridges. 'He just liked his tree house and the cool breeze of an evening and to watch the sunset. That's all he really needed in life.'

Bridges remembers growing up in Kenya as 'like living in a fairytale'.

'It was the kind of life you read about in books. I lived in tree houses and in tents in the bush. My father discovered the area [near the southern Kenyan town of Voi] in the 1970s, when it was a hunting block. There was no mining there until he created it, so when I was a child it was very wild.'

The family lived in harmony with the leopards, lions, buffalo and elephants - even snakes.

Says Bridges: 'The elephants of Tsavo [National Park] are famous. They are gorgeous because they cover themselves in the soil, which is very iron-rich and red. We had a pet python called Patrick who would protect the production from the mines. The local population was quite superstitious about snakes and would not kill them. Often leopards would get into dad's bedroom while he was out and he would come home to find gnawed antelope bones on his bed. The bush was our back garden.'

While it may have been Kenya's beautiful landscape and the company of wild animals that attracted the rugged adventurer, it was his discovery of rare, sparkling gemstones that gave rise to his raison d'?tre. Campbell Bridges had made his name as a gemologist in the 60s, after discovering tsavorite along the Kenya-Tanzania border. The gemstone is considered to be more beautiful than emerald - and some estimates put it at 200 times rarer. He was also involved in the discovery of a blue-purple gemstone known as tanzanite, which is rarer than diamonds.

Campbell Bridges found tsavorite stones in the northeast of Tanzania but couldn't get a permit from the government to mine and export them. His skill and knowledge led him to Kenya, where, in 1971, he discovered more of the stunning gems.

Pavel Sokolov, of the International Coloured Gemstone Association, describes tsavorite as having 'so many shades; it can be a spring-like light green, an intense blue-green and a deep forest green - colours which have a refreshing and invigorating effect on the senses'.

Sokolov says the gem has a high brilliance and durability and is neither burnt, oiled, fracture-filled or irradiated to enhance its colour or clarity. 'It doesn't need such treatment. It's simply a piece of pure, unadulterated nature.'

Of Campbell Bridges, Sokolov says: 'He was a king; a legend among gemologists. I was shocked to hear of his cruel murder. He was always open and friendly and will be greatly missed.'

It's a view shared by jewellery company Tiffany & Co, which, in 1972, named tsavorite after Tsavo National Park, in which it was found. The company featured the man who discovered it in a series of advertisements for the gem in the 70s.

'What Campbell did, single-handedly, for coloured gemstones and the African species of tanzanite and tsavorite cannot be overstated,' says Peter Schneirla, chief gemologist at Tiffany.

Campbell had inherited his love of geology from his father, Rodney Bridges, a Scotsman who was chief geologist for the Central Mining and Investment Corporation, in South Africa. Campbell spent his childhood and studied geo- logy at university in South Africa before moving, in his early 20s, north to what was then Rhodesia, There he worked for the United Kingdom Atomic Energy Authority for a while before moving to Tanzania. He married an American geologist, Judith, and the couple had two children: Bruce and Laura. The family settled at the mining base Campbell Bridges set up 320 kilometres east of Nairobi.

Despite the vast knowledge gained from his studies and gleaned from his father, Campbell Bridge's work - rooting out gemstones in big enough deposits to make them commercially viable - was grindingly tough. He and his emp- loyees would often find tsavorite near the surface that would peter out a few feet further down.

Despite the temptation to dig ever deeper, Bridges says his father always mined safely.

'He employed countless Kenyans during the 39 years he was there. He created jobs that otherwise would not have existed,' he says, adding that his father passed on a multitude of skills and consulted locals to develop a best practice way of working. He says there are many mines dotted around the area that once belonged to the Bridges family.

'[Campbell Bridges] developed the industry. It was created because of him. It didn't exist before he came along.'

Bridges' company, Tsavorite USA, employs about 40 people in the mines, some of whom have worked there for 30 years or more.

'Our last mine manager was with us for 34 years,' says Bridges. 'It's a family business but everyone outside the family who works there is Kenyan. We have not brought in outsiders. We don't just have a mine, we employ people to cut the stones, polish them and grade them - my father was trained to cut stones in Germany. Then there are those who work in the office in Nairobi, who deal with administration. We took nothing outside Kenya apart from the stones, which we sell in America - the biggest gemstone market in the world.'

The mines, leased to Campbell Bridges since 1971, began generating substantial profits in about 2006, when sales of tsavorite to jewellers and collectors in the United States and Europe took off. (The company entered the Hong Kong this year.) Not long after that, the family began to receive death threats from a gang claiming the mines as their birthright and demanding a piece of the action.

'I know exactly who my father's killers are,' says Bridges. 'Three years ago, a local politician came to power in the area and a gangster moved there as well and he formed a mafia. We learnt that he went to the politician and asked for support in taking over our mine - in Kenya, the politicians have direct power and influence over the police. He said we were foreigners and that the gems we were mining for didn't belong to us. The irony is that most of his 'employees' are Kenyan Somalis. They are more foreign than my family.'

Daniel Wesangulap, a reporter on Kenyan national newspaper The Daily Nation, confirms that illegal miners started to operate without licences on the 600-hectare concession the Bridgeses have rights to.

'All the evidence points to an elaborate plan to gain control of the mining of these rare and sought-after gemstones,' says Wesangulap. 'The mines ... had been attracting good money. Even though the ranch owner had a lease agreement with the Bridgeses, the people who wanted a piece of the action moved into the mines anyway.'

The family went to the police and hired a lawyer in an effort to have the illegal miners evicted, but they were not to be deterred.

'They started to threaten us,' says Bridges, 'telling us they would kill us one day. Then about 1? years ago my father was checking one of the illegal mines being run by the gangsters - they are very dangerous because they are not open mines like ours. In front of many of our workers, he was told by the head gangster that if he ever came back to that mine he would not leave alive.'

The threats continued and the family was forced to employ more security personnel. Bridges says his father had been attacked before; when he was with Kenya's commissioner of mines and geology, a gangster approached him and slashed his arm with a knife. About six weeks before he was killed, two of Campbell Bridges' guards were abducted.

'These gangsters took our askaris [security guards] from our mining plains. They told them they were not going to hurt them but would take them to the police and charge them with trespassing. But they had no right to do that because they don't have the surface rights - they belong to another ranch holder - or the mineral rights, which are ours. They told them to tell us that they would be coming for my father's head soon - and also our two heads of security. They said they would kill all three of them.'

Bridges tells of other incidents in which he, his father and staff were attacked and says they reported each of their attackers to the police but no action was taken.

'We have lots of evidence but the police won't back us up because the politician told them not to. He came to power with the promise of returning the mining rights to the Taita people. He said foreigners - not just whites but any other tribes, including Kikuyu [the country's largest ethnic group] - should not have rights in that part of Kenya. That's called majimboism [tribalism] and it's a huge issue in the country. But the irony is another local politician in collusion with him is a Tiveta and so are the two gangsters who started all this. The rest are Somalis. Everyone who works for him is either Kenyan Somali or Tiveta. None are Taitas.'

The Bridgeses wrote down a list of names of people who had been threatening and attacking them and who they believed to be ringleaders, which they gave to the police.

Two junior officers tried to help until 'somebody got to them'.

'The police say they have arrested the mastermind - but he's only mid-tier, they got the sacrificial lamb,' says Bridges. 'They ignored our information because they are afraid.'

The inspector in charge of the case, Kenneth Karume, did not reply to requests to comment for this article.

Then came the fateful day in August.

'A mob of gangsters ambushed us as we drove to our mining camp,' says Bridges. 'They'd blocked the road with trees and bushes, forcing our truck to stop. About 30 men ran down the hill towards us shouting in Swahili, 'We're going to kill you.' Then several of them started attacking us with machetes, spears, knives, clubs and bows and arrows.

'My father was stabbed in the chest and I saw him fall to the ground. Two of our security guards were repeatedly slashed with pangas [broad-bladed cutting tools] and they received terrible injuries. We just kept on fighting back and eventually they ran off and I managed to get my father in the truck and drive him to a clinic. But it was too late.'

The autopsy showed Campbell Bridges had been stabbed through the heart.

Despite his father's death and the threats to his own life, which continue, Bridges will not be driven away from his home and his legacy.

'I've spent most of my life at the mines. I went there with my father as soon as I could walk. We would go on prospecting safaris together all the time with my mother and my sister. One of my earliest memories of my father was prospecting with him while riding pillion on his motorbike.'

Bridges says he loves Kenya but hates 'certain aspects of it' and he is determined to see his father's killers brought to justice.

'We have what is probably the best documented murder in history, with evidence and witnesses. But nothing is being done about it. That's disgusting,' he says. 'My father gave so much to Kenya, both in international recognition and investment, not to mention his own sweat and - in the end - his life.'

Not only is it a personal crusade for justice that Bridges is embarking on, he is also determined to stamp out the illegal mining and dealing of tsavorite in Kenya.

'I believe 80 to 90 per cent of the tsavorite coming out of the country is illegal,' he says. 'They are basically blood stones. Foreign dealers will fly in without licences. They'll sit in a town for a few days where they'll have the rough stones brought to them and they'll hand over a stack of cash, stick the illegally mined stones in their suitcase and simply get on a plane and leave the country. The gangsters who sold them the gems will pocket the cash and the rest of Kenya sees nothing.'

Bridges is calling for a certification scheme for tsavorite similar to the Kimberley Process for diamonds, which was set up in 2003 by the United Nations to ensure consumers would not be duped into purchasing 'blood diamonds' (those used to finance a war or connected to human rights abuses). The trade in these illicit stones fuelled decades of conflict in countries such as Angola, Ivory Coast, Democratic Republic of Congo and Sierra Leone (which was the location for the 2006 Hollywood film Blood Diamond, starring Leonardo DiCaprio).

Says Bridges: 'I'd like to see an embargo until that sort of process can be set up for the gemstones of Kenya, especially for tsavorite, which is the biggest and most valuable coloured gem in the country.'

In an effort to ensure its gemstones can be recognised, Bridges' company is now putting a laser engraved serial number on each stone, which are logged on a database.

'It's so purchasers know exactly where that stone came from - so they can track the route from mine to market,' says Bridges, who was reluctant to resort to such stringent measures because of the cost and the extra work involved.

'The last thing my father said to me was that he was so disappointed. But he was an optimist. I would ask him if it was wise for us to stay in Kenya with all that was going on and he replied that he had spent his life trying to create something good for Kenya and that it was where he belonged. He believed that we should see everything through legally and through the right channels and no matter where we have a road block, we'll find our way around it and we'll take it to another, higher channel. He was tenacious and always believed it was possible to change things for the better.'

In February, the UN published a report, the most damning yet, which included evidence of systematic and widespread police abuse in Kenya. Professor Philip Alston, the author of the report, described the police as a law unto themselves and said they often killed with impunity.

Alston says: 'I have received overwhelming testimony that there exists in Kenya a systematic, widespread and well-planned strategy to execute individuals ... Most troubling is the existence of police death squads operating on the orders of senior police officials.'

Bridges says since his father's death, the Kenyans where he lives are more in fear of their lives than ever.

'All the neighbouring miners would come to my father for help and advice. They looked upon him as the father of mining in Kenya. Since this has happened to him, they are wondering what's going to happen to them. Will they be next?

'My father's death was a tragedy in so many ways. He was an adventurer. People called him the real-life Indiana Jones, and he was. He would say: 'Bruce come look at this flower, look at this cloud - I see a dragon in it; look at this butterfly's wings and notice how gorgeous the pattern is. How lovely would it be if we could create a piece of jewellery like that from tsavorite?'