INTRODUCTION TARA BROWN: They're remarkable creatures. Social, intelligent, at times, very human. And just like humans, elephants experience many complex emotions. Take them away from their close-knit family herds and they'll descend into deep depression, push them too far and they'll snap. Which makes our heartless treatment of these beautiful animals all the more confounding. Hunting them to extinction, forcing them to perform in circuses, locking them up in zoos. No wonder they can become killers. But even the most traumatised, the most violent of elephants can be saved. Tonight, Elizabeth Vargas takes us to a wonderful sanctuary where they're healing these gentle giants. I should warn, some viewers might find certain images confronting.

STORY ELIZABETH VARGAS: If you were ever lucky enough to encounter a healthy herd of elephants in the wild, it is a wonder to behold. In South Africa, on the MalaMala Preserve near Kruger National Park, I rode close to a group of some 40 elephants with camp manager, Tom Bloy.

TOM BLOY: They're very, very tight family groups, led by the oldest female, the matriarch. They, they stick together for as long as they, they survive. 50, 60 years the adult female might last.

ELIZABETH VARGAS: For the elephant, the herd is home. It is family. Elephant researcher, Gay Bradshaw - GAY BRADSHAW: The herd is the most important component of elephant culture. They're very affectionate with their children, with each other. Always touching and talking to each other. They have a culture that they pass on through generations. They even have grieving rituals - When someone in the family dies, people gather around. They touch the body. They come back days later, months later, even years later, to visit the body. They bring their children back to visit the body. So, essentially, a healthy, happy elephant is one where humans are not interfering in their lives.

ELIZABETH VARGAS: If elephants are wary of human encroachment, there is ample reason. The great African herds have been decimated over the last few centuries, hunted down for their ivory tusks. The scenes of such slaughter have been fully documented. But experts say the trauma the surviving elephants carry with them is only now being fully understood. Particularly the youngest survivors, who often have the added trauma of being shipped off to zoos and circuses around the world. These are the lucky ones - the baby elephants that have survived the slaughter of their family's herd and have been rescued.

DAPHNE SHELDRICK: When they come in, newly orphaned, they have nightmares at night, they wake up screaming, they can't sleep very well. They're all psychologically disturbed.

ELIZABETH VARGAS: Daphne Sheldrick has devoted her life to elephant well-being and survival. This is the elephant orphanage she runs in Nairobi, Kenya. The babies could never survive in the wild without the protection of the herd and without fresh milk.

DAPHNE SHELDRICK: Here in the nursery, the infant elephants will follow the keepers wherever they go, because the keepers are the family.

ELIZABETH VARGAS: The keepers even sleep with the orphans at night, never leaving them alone, teaching them to trust again. To help the healing, they're taught to play games like soccer to form new social bonds with each other.

DAPHNE SHELDRICK: When you actually raise them and you're part of their family for 10 years, every day and every night, then you start to understand them. You must never, ever be cruel to an elephant because they have an amazing memory, and they will remember that for life. And they bear grudges.

ELIZABETH VARGAS: And that can lead to this. Approximately 600 elephants live in captivity in the United States. Most were born in the wild and taken from their families and brought here to live or work in our zoos and circuses.

GAY BRADSHAW: Most of the elephants that we see have had a succession of very severe traumas. They have seen their family killed, or they have been taken away from their family. So, when science says elephants are just like people - they feel like people, they think like people, they act like people, they have a sense of self like people - it compels us not to treat them as property.

ELIZABETH VARGAS: Many zoos and circuses treat their elephants very well. But in the best of circumstances these animals live lives of confinement. And performing elephants have often been trained brutally and aggressively.

GAY BRADSHAW: The kinds of beatings and the kinds of physical deprivation they've experienced is with them just like it would be a human being.

ELIZABETH VARGAS: It was August 1994, when the circus came to town in Honolulu, Hawaii and the audience became witnesses to this horror. The elephant, Tyke, snaps, kills her trainer, and then runs out to the city streets.

GAY BRADSHAW: The Tyke footage is very disturbing. The behaviour that Tyke displays is someone who is so traumatized and so upset, very unelephant-like behaviour.

ELIZABETH VARGAS: In India, an elephant kills its trainer and attacks another elephant.

GAY BRADSHAW: So, when you see an elephant bursting out, acting aggressively, killing, it's totally unprecedented.

ELIZABETH VARGAS: For Gay Bradshaw, these sudden acts of violence, often seemingly unprovoked, became a subject of a study published in 'Nature'. In it, she drew direct parallels to post-traumatic stress disorder, a most human condition and diagnosis.

GAY BRADSHAW: To diagnose an elephant with post-traumatic stress disorder is novel but that's because we have denied elephants the capacity of having a mind, having a psyche, having emotions. But basically, the neurobiology or the neuroscience says, "Yes, it's there, the potential is there, "and the behaviour confirms it."

ELIZABETH VARGAS: These are the sounds of elephants talking to each other. The trumpeting and the low rumbling can be heard for miles over the countryside. This is The Elephant Sanctuary, and it's not in Africa. It's a 2,700-acre private reserve in rural Tennessee, just south of Nashville. It is a last refuge for abused or neglected elephants, where they come to live out their days and to heal.

CAROL BUCKELY: This place is for the welfare of elephants. This is not about people. They need to be in a safe place. They need to be out of environments where they're abused.

ELIZABETH VARGAS: Carol Buckley and Scott Blais have worked all their professional lives caring for elephants. And in 1995, they founded the sanctuary. The public is not allowed here, only the small staff that cares for the herd, knowing the risks they face. Every elephant here has a troubled history. Some have killed their keepers or trainers.

CAROL BUCKELY: That's Debbie. That's Ronnie. Way back there, Billy, Liz, Frida.

ELIZABETH VARGAS: This was Debbie and Frida in 1995 on a rampage in Hanover, Pennsylvania, crashing through the front windows of a car dealership. Other elephants at the sanctuary have less violent histories, but most have suffered from abusive care. Meet Sissy and Winky. Sissy had previously killed a keeper at a zoo in Texas. And then, there's Winky. She had attacked trainers several times at a Wisconsin Zoo and had a reputation as being dangerous. They are now approached only by the people they know and trust. I am asked to keep my distance.

SCOTT BLAIS: This is their space. We are entering their space. It is a risk that we take, that we are aware of.

ELIZABETH VARGAS: You can go up to these animals sometimes and pet them. They hug you. Do you ever forget for a moment how powerful they are and that in a second...

CAROL BUCKELY: Never. Never.

ELIZABETH VARGAS: To watch Carol and Scott with the elephants is remarkable. There is great affection and constant physical attention. Elephants need the touch. They love to have their tongues rubbed and they appear to be quite peaceful and happy to be back in the herd again, free to walk where they want. But they also carry deep scars. Sissy forever carries a tyre around that is a kind of security blanket that somehow makes her feel safer.

SCOTT BLAIS: When she first came, she wouldn't go anywhere without it. She has many tyres now. They're scattered all over the place.

ELIZABETH VARGAS: It is a need to belong and befriend, that is the key to the elephant's sense of well-being. And there is no greater proof of that than this unforgettable encounter nine years ago, filmed at The Elephant Sanctuary. Shirley had performed in the circus her whole life. And years earlier, she had befriended a much younger elephant named Jennie. For just two weeks, Shirley had mothered Jennie, until they were separated again for the next 22 years. By chance, they would find each other again. And this was their reunion.

CAROL BUCKELY: Shirley sort of stopped for a moment, glanced to the side, looked at Jennie, and then it was like her eyes lit up And then they both started vocalizing.

ELIZABETH VARGAS: The two elephants needed to get to each other. They reached through the bars to touch each other with their trunks, to re-establish a most intimate connection. 22 years later, for an elephant to remember the... the one that mothered her and took care of her is pretty extraordinary. What does that tell you?

CAROL BUCKELY: I think it just reinforces how highly intelligent these creatures are and how very, very emotional they are and how important emotions are in their lives.

ELIZABETH VARGAS: For the next 7.5 years until Jennie died, Shirley continued to mother her, standing over her as she napped to provide shade, rarely leaving her side. Now, in its 13th year, the Sanctuary is home to 17 elephants, with a capacity to grow to nearly 100. What do you think the cure of the Sanctuary is?

CAROL BUCKELY: It's the elephants having elephants. The elephants heal each other, and it's family. It's because they're creating a family. They may not recover completely, but they will recover.