Fossey, an American primatologist and conservationist known for undertaking an extensive study of mountain gorilla groups over a period of 18 years, was brutally murdered in her cabin at a remote camp in Rwanda in December 1985.

It has been theorized that her murder in 1985 was linked to her conservation efforts.

And now a new documentary is set to present a new theory on who killed the 53-year-old.

Dian is claimed to have tied up hunters, smeared them with gorilla dung, and whipped their testicles with stinging nettles, according to the Mirror as Birmingham Mail reported.

She is even said to have kidnapped one poacher’s son – but her determination to protect the gorillas she loved led to her downfall.

She was found murdered in her mountain cabin in Rwanda on Boxing Day.

Dian with Gorillas in Rwanda

A new National Geographic documentary , Secrets in the Mist, says her scientists and US diplomats­ in Rwanda believe officials who feared she would expose their links to poaching and gold smuggling were responsible.

When Dian, who never married following a failed romance, began studying gorillas they were seen as monsters, but her work revealed a softer side to these gentle giants.

She first encountered mountain gorillas on a seven-week trip to Africa and abandoned her career as an occupational therapist to set up the Karisoke research centre in Rwanda in 1967.

Lacking any scientific training, Dian struck up a unique bond with the apes. Awestruck locals called her “the woman who lives in the forest without a man”.

She even adopted one group of gorillas, naming the silverback after her beloved Uncle Bert and a female after her aunt Flossie. She also nursed two orphans Coco and Pucker back to health after they were injured by poachers who planned to sell them to a German zoo.

But her favourite was a young gorilla with a broken finger she named Digit, who loved to play with her. When Digit was killed and his head was hacked off by poachers on New Year’s Eve, 1977, she was overcome by grief and anger.

“I don’t think I’ll ever get over it,” she wrote. Months later Uncle Bert was shot through the heart and a female, Macho, killed.

Dian’s new family disintegrated.

She feared the remaining gorillas faced extinction from increased poaching for trophy skulls, gorilla hand ashtrays and baby apes. So, it is said she resorted to more extreme tactics.

Dian wore a halloween mask to pose as a witch and chase off poachers who believed in black magic and began to pay armed guards to protect the gorillas.

When guards caught a poacher she would interrogate and humiliate­ him. She even threatened­ to hang one hunter.

Researcher Amy Vedder said: “When we arrived at Karisoke we didn’t realise we’d be asked to do aspects of anti-poaching. It wasn’t something we were comfortable with.”

Eventually Dian went too far, confronting a poacher in a nearby village and demanding his gun.

When he refused she vandalised his house and threatened to kidnap his son. Fellow scientist Ian Redmond said: “She brought the boy to the camp.”

Next day Dian returned him but it was too late. She was prosecuted and fined. With so many enemies she was forced to go back to the US to teach and raise awareness about the plight of the gorillas.

By the time Dian raised enough money to return, the government realised the gorillas could attract wealthy tourists to Rwanda and was trying to protect them.

It resented her interference more than ever, especially after she fired a pistol over the heads of “pompous” US tourists, fearing they would infect­ gorillas with human diseases.

Frustrated at being frozen out, Dian threatened to show the world evidence of poaching and gold smuggling in Rwanda’s national parks.

Her friends believe that implicated­ several government officials­, and that one arranged her murder. Her centre was near prime gold smuggling routes across Africa.

A letter about gold smuggling she sent to Redmond weeks before her death never arrived, but a copy was found in her files, fuelling suspicions of a plot.

Diane was found with her head caved in “like broken glass”, machete marks across her face, a pistol by her side.

Her cabin had been ransacked, but no money or weapons stolen, effectively ruling out poachers. The evidence suggested she was killed elsewhere and her body dumped to frame her team. It worked.

Police charged her assistant Wayne McGuire with murder to steal her research helped by tracker Rwelekana.

Fearing foul play, the US embassy smuggled­ McGuire home. Rwelekana died in jail, supposedly suicide, though guards believe he was murdered to hide the truth.

McGuire said: “Dian believed she was going to be killed. She said if you ever hear firing at night, don’t worry about me.

“Just get out as fast as you can. I didn’t kill Dian. I was her friend and had everything to lose from her death.” 

Dian was buried next to her family, including Digit and Uncle Bert.

Any clues to who really killed her were lost in the Genocide against Tutsi in Rwanda in 1994. Her student Kelly Stewart said: “I don’t think we will ever know what happened, but she’d have written that ending.”

Another ending Dian would enjoy is her legacy. Today there are 880 mountain gorillas, up from 280 when she died.

Sigourney Weaver, nominated for an Oscar for playing Dian in Gorillas in the Mist, said: “I think Dian would be delighted and optimistic about the gorillas.”