When British filmmaker Orlando von Einsiedel set off to eastern Congo to start filming a documentary about Virunga National Park, he wanted to tell a positive story of rangers saving endangered mountain gorillas from poachers.
Little did he know that his film about the park would become an exposé of the corrupt ways of an international oil company that had set its sight on the park, a UNESCO World Heritage site.
"I came across the story of the rangers (of Virunga)... and I thought the story of the park could tell a bigger story of the rebirth of the entire region," von Einsiedel told Thomson Reuters Foundation in an interview in New York, where the film premiered at the Tribeca Film Festival last week.
As he started working on his project, he learned about an oil company's controversial operations in the area.
The Congolese government granted UK-based Soco International permission to explore for oil in 2010, despite strong opposition from environmental and civil society organisations as well as the UK government.
Fifty-two percent of the concession Soco was granted - a portion of land called Block V - is located within the park borders, and opponents say that oil-related activities in Virunga are illegal.
With help from French journalist Melanie Gouby, von Einsiedel secretly filmed company contractors and supporters as they attempted to bribe park staff in order to obtain access for the firm's operations.
A hidden camera filmed one company manager saying that Congo needed to be recolonised, and that Congolese people were incapable of administering themselves and their country.
After the film was screened in New York, Soco released a statement denying that its ongoing operations in Virunga Park are illegal.
"Soco believes that the film misrepresents its activities in Block V and does not accurately portray the company's track record... of responsible operating," the company said in a statement.
The company also stressed that its exploratory operations won't affect the area of the park that is home to a quarter of the 880 mountain gorillas left in the world.
"Soco's only planned activity continues to be the scientific studies involving environmental baseline studies, social investment projects and a seismic survey of Lake Edward due to start shortly. No drilling has been planned or is warranted at this stage," a statement on its website said.
"I think the issue is that this company has a serious lack of oversight about what it's doing on the ground... and that's incredibly worrying," von Einsiedel said.
NOT JUST OIL
Oil isn't the only threat to the park's survival.
A few weeks into filming, fresh fighting erupted between the Congolese army and M23 rebels - the latest incarnation of the Tutsi-led insurgents who have battled the government in its mineral-rich eastern region since 1996, in a conflict that has caused the deaths of millions from violence, hunger and disease.
"Frankly, there were moments when I was absolutely terrified, but I think what I always took away from it is how the rangers were dealing with that for the past 20 years," von Einsiedel said.
The Congolese government and the rebels signed a peace deal in December.
Defending Virunga is notoriously risky business. According to the park's website, more than 130 rangers were killed protecting the natural reserve and its gorillas.
Earlier this month, the park's director Emmanuel de Merode, a member of the Belgian royal family and one of Africa's leading conservationists, was shot four times on the road linking the park's headquarters in Rumangabo to Goma, the capital of North Kivu province.
De Merode, who features prominently in the film, is now in stable conditions and recovering at a hospital in Kenya's capital Nairobi, according to von Einsiedel.
In one of the film's most tense scenes, de Merode is shown leading the park's rangers as they organise to defend Virunga from fighting between the Congolese army and M23 rebels.
The documentary also shows the deep bond of affection between rangers and the gorillas.
Von Einsiedel stressed the importance of raising awareness about the shady dealings that are threatening the park.
"If Virunga folds in the face of business interest, where does that leave other protected sites?"