Our son is in an African jail for stumbling on a mass murder

David Simpson could not have been happier. Having left behind his family farm on the edge of the North York Moors, the 24 year-old was working for an exclusive safari company in the Central African Republic.

He was tracking herds of antelope and elephants, living in the forest camp and flying clients across the country in his light aircraft.

Now he is in a grim African prison. Simpson, from the small village of Gillamoor, is languishing in a cell in Bangui - the capital of one of Africa's wildest, most corrupt and least developed countries.

He had stumbled across a massacre, finding 18 bodies in the lawless south-east of the country, and reported it to the police. But to his horror, and that of his parents, it was Simpson who was charged.

"I just keep on thinking, 'How can this be happening?' said his mother Vicky, 53, sitting in the conservatory of the family home, which has views of rolling hills. Their four black labradors lolled at her heels, and the immaculately kept house was filled with flowers from friends and wellwishers.

"In the rest of the world it would never have even got to an investigation, let alone being put in prison," she said. "I was happy that he was out there, because I knew he was happy. But I never expected this." Simpson's sister Helen, 17, added: "Here you are innocent until proven guilty. Out there it seems to be the exact opposite."

The family can talk to him on his mobile phone, and say he is resilient but desperate to get out. It could take a year for the case to come to trial. Last week he was moved from Bangui's police cells to the country's main prison, where he shares a cell with around 60 other prisoners.

They cannot lie down without elbowing other inmates and there is no food provided. Simpson, who is being held with his boss Erik Mararv, 27, relies on food brought by Mararv's sister.

On Friday the Foreign Office said it had registered a formal complaint with the authorities in Bangui. But the family is angry that the British authorities have been so slow to act since Simpson reported the murders on March 23 and was imprisoned on March 29.

"It's been amazing how little the Foreign Office has done," said his father Peter, 54, who rears pheasants and partridges for shoots. "I'm a straight-talking Yorkshire gamekeeper, so I told them in no uncertain terms that they had to do something. He's a good lad and it's not right that he is in prison for reporting a crime."

His son was passionate about his work in the Central African Republic - despite having scarcely set foot out of Yorkshire before.

For his 18th birthday his parents had bought him flying lessons, and he relished the experience. But he was working at a door factory in Sheffield and hated city life.

He was unsure what to do with his life. Then, in 2010, he saw a documentary about managing safari farms in Africa, rounding up and monitoring animals by plane. He emailed the producer, and two months later was starting a new life in a country which he had previously not heard of.

His role was to fly over the jungle which carpets most of the country, spotting new herds and watering holes.

When the sites were identified, the safari company Cawa would set about building roads and setting up the camps to work in that area. Big-game hunters would flock to the country, paying in excess of pounds 40,000 for a fortnight to shoot animals such as the giant eland or the bongo - both huge, beautifully-striped antelopes. Leopards, lions, buffalo and baboons also populate the lush forest.

With there being almost no roads, Simpson would fly the guests in his light aircraft from camp to camp.

"I had never seen him so happy," said his brother Paul, 22, who visited him. "He had a pet monkey and was learning the local dialect, Sangho. He believed his work was really important. If the hunting company didn't exist then poachers would wipe out a lot of the animals, killing them for the meat and hides. Two thirds of the people in the village with the camp rely on the company for their livelihoods. He absolutely loved it out there."

On March 23, Simpson was exploring a remote area in a region thought to be run by the Lord's Resistance Army.

The militia, headed by the self-styled messiah Joseph Kony, has terrorised Uganda, Sudan and the Democratic Republic of Congo for 25 years, murdering thousands and abducting an estimated 20,000 children to serve as soldiers.

With his African colleagues, Simpson was looking for signs of wildlife. Instead they found the remains of 18 villagers who had been tortured with boiling water and hacked to death with machetes.

The Yorkshireman knew many of them, having worked in the villages. One of his African colleagues recognised his brother. Another saw his cousin among the dead.

The men went to get the police. But they were dismayed when officials took one photograph on a mobile phone and left. The situation took a dangerous turn when the military then told local people that the safari company had killed their men.

"He realised the situation was turning, so he ran to his plane but they were chasing him," said Paul. "He was fired at while he was taking off. The locals then burnt the truck and looted one of the depots. It was chaos."

Mararv, a Swedish citizen born in the Central African Republic, voluntarily went to the police in the capital to assist their investigation. But he was arrested, and several days later Simpson and 13 local staff were also detained. They suspect that they are being held because officials hope to obtain huge bribes.

"The justice minister told us they could be free for euros 1?million [pounds 800,000]," said Paul. "It's a joke. They see white people and think we are the money tree."

Simpson is hoping international pressure will speed up his release. Despite his ordeal, he is keen to continue his work in Africa, and his family wants to travel there.

"I'd like to go and visit him, and I think we might go in January," said his mother. "But I think we need to sort this mess out first."