On a bright, sunny morning in the summer of 1973, Ron and Paula Watson, two farmers in Springfield, Missouri, witnessed something that changed their lives forever.

It was an alien abduction, they say. But not of a human – of cattle.

They said they saw a 'green, cone-shaped craft' – next to which two 'silver little beings' were standing over a large black cow.

'I told Ron, 'My god, they got a cow! What are they doing to it?' Paula said. 'It had its eyes open and its tongue was like, hanging out a little bit. But it just laid there and it didn't move.'

She described in detail how she saw the aliens running their hands over the cow and then inspecting their long fingers before they 'floated' it into their large ship in the distance.

Their neighbors never believed their story, though one did admit to having one black cow left unaccounted for. The Watsons' story sounds like something out of an early science-fiction film – but it became one of many stories of alien and UFO sightings used to explain the thousands of cow mutilations reported across the United States in the 1970s.

Since the 1970s, bizarre murders and mutilations of cattle have been reported across the nation, primarily in the Midwest. In this photo (left) of a cow in Saguache County, Colorado in 1975, a female cow's utters have been removed with surgical precision. In the image on the right, a cow was found with its tongue removed in July 2013 on a farm in Missouri

News reports make up the bulk of the FBI's 32 page report on the subject, which is prefaced by a brief explanation that their investigation was hindered by a lack of jurisdiction in most cases

Within the depths of the FBI's database of unsolved mysteries lies the graphic tale of these cattle murders, which outraged and petrified farmers for decades, and is still continuing today.

Speculation surrounding who – or what – might be responsible for the killing and mutilation of thousands of cows has ranged from satanic worshipers, government agents, and even aliens.

The most curious aspect is not that the cattle have died, but the way in which they did. Since the early 1970s farmers have discovered their treasured (and expensive) animals dead with various organs excised – including eyes, noses, tongues, hearts, livers, anuses, and genitalia removed with laser precision.

Though many theories have been offered it's a phenomenon that no one – not even the FBI – have ever been able to solve.

In 1974, newspapers started to catch wind of these bizarre mutilations, which first took place primarily in extremely rural farmlands in the Midwest. Instances were reported across the nation but were mostly scattered among South Dakota, Colorado, Kansas, and Nevada.

The news reports make up the bulk of the FBI's 32 page report on the subject, which is prefaced by a brief explanation that their investigation was hindered by a lack of jurisdiction in most cases.

The FBI told DailyMail.com that this was due to the fact that at the time there was no federal law declaring animal mutilation a federal crime, which didn't allow the department to continue investigating.

Many residents reported seeing helicopters circling the areas where cattle later turned up dead and sliced up with seemingly surgical accuracy. This prompted concerns that the mutilations, nicknamed 'mutes' by those familiar with the subject, were being propagated and covered up by the government.

in this image on the left, the cow's heart was excised with expert care - and was the third of three cattle mutilated on the same farm in Missouri beginning in 2011. Theories of who, or what, might be responsible have ranged from satanic cults, aliens, and the government. In the image on the right, ranchers found an animal with its sex organs and anus removed

Linda Moulton Howe is a former Miss Idaho turned investigative journalist and regional Emmy-winning filmmaker who has been a primary proponent of the 'alien argument'

This was around the same time of the height of alien paranoia in the United States – when UFOs, or balls or discs of floating light, were being spotted in similarly rural areas, often preceding or following the cow mutilations.

Many who have dedicated their lives to the subject believe, in fact, that aliens are responsible for the mutilations and that the government has been attempting to cover up their crimes (and existence) for years.

One such person is Linda Moulton Howe, the regional Emmy-winning filmmaker who the Watsons shared their story with for her documentary Earth Mysteries: Alien Life Forms. She has been one of the most steadfast supporters of the alien argument.

Her research conjures the images of what we picture as the stereotypical alien abduction – flying saucers beaming animals up into space with light.

At least two people even reported being abducted by aliens at that time – including one woman named Judy Doraty and her daughter Cindy.

In a 1990 symposium proceeding Howe wrote: '…I found in so many eyewitness accounts of orange glowing objects the size of football fields hovering above pasturelands where mutilated animals were later found. Or beams of light observed shining down from 'silent helicopters' that lighted pastures 'brighter than daylight' and the next day mutilated animals were found. And eyewitness reports of strange craft and/or non-human creatures involved with animals.

'There was Judy Doraty who in 1973 watched a brown and white calf rise in a pale beam of yellow light. Inside the craft, she saw tissue cut from the eye, tongue and testicles by two small grey-skinned creatures. They had four fingers, instead of five, and those long, thin fingers tapered into dark nails. Their eyes had vertical pupils like a cat or a crocodile's.

'Judy's daughter, Cindy, also described in a 1990 hypnosis session seeing a calf rising in a beam of yellow light.'

In a rare winter mutilation, this calf was found in Hooper, Nebraska in 1975 with its jaw completely cut out all the way up to its right eye socket. Eyewitnesses often reported seeing beaming lights or suspicious helicopters near where mutilated cows were later found

US Senator Floyd Haskell from Colorado pleaded with the FBI to become involved with the mutilations in August 1975 after receiving more than 130 cases in the state alone, and farmers had taken to arming themselves out of fear

Supernatural explanations were the only ones that made any sense at the time – given that the technology of the era was not advanced enough to have performed what appeared to be the use of localized lasers.

The areas surrounding the excisions, often around the anus of the murdered animals, had a blackened and burned appearance to them – suggesting the use of a high-powered laser. Other researchers, however, proposed different conclusions.

Christopher O'Brien, an author and investigative journalist on the subject, said that in his 200 cases of dealing with cattle death, about 40 of those were done by 'something with intelligence'.

Christopher O'Brien, an author and who has investigated the subject for decades, said that in his 200 cases of dealing with cattle death, about 40 of those were done by 'something with intelligence'. He is pictured researching left in 1993 and right in 2012

This Hooper, Nebraska calf also had its anus cut in a 10-inch wide diameter and 18-inch deep. O'Brien told DailyMail.com that he didn't believe aliens were responsible - because 'who would fly thousands of light years to collect cow butts?'

He is more skeptical of the alien explanation – saying that Howe's research doesn't incorporate many of the scientific findings that have been made.

He told the DailyMail.com that when a cow decomposes, the vegetable matter contained in one of its four stomachs makes the animal bloat. As the moisture leaves the body it then starts to deflate – causing the exposed edges of the animal to stay hard and darkened.

'To someone who doesn't know what they're looking at – it looks like a burn,' he said.

O'Brien feels that the alien argument is one used to sensationalize the topic and are only looking at a small portion of the total data.

He can't deny, however, how disturbing the number of 'high strange' cases are that he's seen – the ones that involve otherworldly circumstances.

On one occasion which O'Brien calls his 'strangest case' – he was called to the scene of a mutilated calf in Del Norte, Colorado.

'It was really freaky, it wouldn't rot,' he said. 'It was found in a complete pristine, five inch snow field without one drop of blood on the snow. All the blood had been taken from the animal. The heart and liver had been expertly excised and left in the body cavity.

'The chief medical veterinary pathologist said "it wasn't an animal that did this",' he continued.

In O'Brien's book, Stalking the Heard, he writes that the month-old calf was also missing its spine from the hips to the skull and the brain was gone. It's right front leg was also gone, and the vast majority of its ribs, both eyes, ears, intestines, reproductive tract, and lungs had been removed. Its rectum was also mutilated.

Two witnesses also reportedly saw a large beam of light near the house the previous evening before the calf was found.

O'Brien's 'strangest case' was this month-old calf that was missing its spine from the hips to the skull and the brain was gone. It's right front leg was also gone, and the vast majority of its ribs, both eyes, ears, intestines, reproductive tract, and lungs had been removed. Its rectum was also mutilated and its heart and liver were excised but left inside the body cavity

He hits on another popular argument for the cattle deaths – though arguably the least plausible explanation. Many believe that the excisions were being done simply by other animals – scavengers such as vultures or coyotes.

O'Brien is quick to discredit this based off of his own experience.

'The first thing I look for is cut hair follicles,' he said. 'When birds or coyotes rip they rip between the lines of hair they don't cut the hair. If I find a 2-3 inch section of cut hair follicles I know that someone or something with a sharp implement did that. It wasn't done by birds or scavengers.'

These 'high strange' cases are less likely to be reported by ranchers, according to O'Brien.

'The freakier the case the less likely the rancher is to report it – they're so freaked out they won't even tell their family or neighbors. He doesn't want people in the community to think he's been singled out and victimized by some supernatural thing. That's why they're very reluctant to come forward.

'It's only when they see the hundreds and hundreds of helicopters being reported around these sites – mostly military helicopters – it's only when they see that that they feel like they've been targeted or victimized by their government and that pisses them off.'

Though the occurrences in the United States have considerably slowed down since they were at their height in the early 1970s, they certainly haven't stopped. O'Brien notes that they have seen a consistently high number of cases in South America, especially Brazil and Argentina.

O'Brien says that throughout his decades of studying mutilations, he's noticed that there's been a shift to South America, where he believes they've had more than 4,000 cases since 2002. A news report included in an FBI briefing stated that more than 1500 cattle in 22 states were killed and mutilated from 1973 to 1976 in the United States

He claims that since 2002, there have been more than 4,000 cases of cattle mutilation in South America - and are still reporting anywhere from three to a dozen cases a week.

Back in the United States, just before the New Year in 2016, and again a few days afterwards, two cows were mutilated in nearby rural towns in Kansas.

In McPherson County, Carla and John Shearer discovered one of their pregnant cows dead with one eye removed and both her top and bottom eyelids and eyelashes excised.

'We lose animals, but not like this,' Shearer told the Kansas Agland. The couple believes whoever killed their $4,000 cow used a tranquilizer or stun gun to immobilize it before killing it.

'She died in motion – she was walking and she just went straight down,' Shearer added.

Carla and John Shearer on McPherson County, Kansas discovered one of their pregnant cows dead with one eye removed and both her top and bottom eyelids and eyelashes excised in January 2017

The bull found in nearby Harvey County was found dead with its genitals removed – also cut with surgical precision.

It is O'Brien's opinion that the mass mutilations – of which there were thousands reported in the 1970s alone – are a part of a secretive government effort to research animal plagues such as mad cow or prion disease.

'We've seen this many, many times throughout history – where one case will happen and then within a week there will be a dozen. I think they're looking for something – that's the best explanation I can give. And I think they're looking for something within the food chain.

'Bovine spongiform encephalopathy is the most horrendous affliction that you could possibly imagine. It's 100% fatal – it produces large holes in the brain tissue and creates holes like Swiss cheese in the neuron system and the brain synapses start to misfire. You forget to breathe and your autonomic system starts to break down.

'That I think is the basic underpinnings of it – we're dealing with a group that is interested in keeping an eye on the food chain. The beef industry is the largest, most powerful industry that you never hear about. I think we're dealing with something that's being protected by some quasi-governmental group,' he said.

Though tempting to indulge in the possibility of space creatures invading the planet to study our animals, O'Brien finds this explanation a bit too impractical.

'It sounds like bad science fiction,' he said. 'Who would fly hundreds of light years to come and gather cow butts?'