(CNN) -- Images of chimpanzees on television or in the movies depict cute, cuddly and smart animals. So it's no wonder that some people, perhaps those with exotic tastes, may seek them out as pets.

A chimp comes up to the fence to inspect visitors at an animal sanctuary in Fort Pierce, Florida.

Some chimp owners will even dress the animal in diapers and treat them like a doll or a child.

But playing that way with chimps is risking lives, the president of the Humane Society of the United States said.

Wayne Pacelle wants people to know that chimps kill in the wild.

"Their behavior, which is born into them, can come out even if you put the animal in a bed at night, even if you dress them up in a tutu. They are still wild animals," he said.

Pacelle's organization estimates about 15,000 monkeys and other primates are living as either pets or in private zoos.

"As infants they are fascinating," said Beth Preiss, who directs the organization's Exotic Pet Campaign. "But they grow up and become dangerous to manage."

Just how dangerous was demonstrated Monday when a pet chimp named Travis attacked his owner's friend in Stamford, Connecticut.

When Sandra Herold couldn't pull her nearly 200-pound chimp off of Charla Nash, she tried to drive him away by stabbing him with a butcher knife and hitting him with a shovel.

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When that failed to stop the vicious attack, Travis' owner -- heard on a 911 tape -- asked the police to shoot the chimp in order to stop the attack. They did and Travis died of gunshot wounds. The victim of the attack remains hospitalized with extensive injuries to her face and hands.

While being raised by Herold, Travis was treated like a member of the family.

"I cooked for him, I shopped for him, I lived with him, I slept with him," Herold told WNYW.

Preiss said she believes the only place primates should be sleeping is under the stars. "When chimps are kept in captivity we think they should be kept in as natural environment as possible," she said.

One of those seminatural environments for chimps raised in captivity is operated by the nonprofit organization Save The Chimps. The sanctuary in Fort Pierce, Florida, has several three-acre islands among 200 acres of wilderness where 150 chimpanzees roam free.

The chimps arrive from different types of captivity. Some are former pets, but there are also some descendants of NASA's space chimps and some chimps used in labs for medical research. Watch what life is like for the animals at the sanctuary »

It is the former pets that have the hardest time adjusting, according to Jen Feuerstein, director of operations for Save the Chimps. "We make them dependent on human beings for their survival," Feuerstein said.

Travis was 14 years old when he attacked, six years older than the age chimps used for entertainment are usually retired. They are adorable as babies but "when grown, they are seven times stronger than an adult human and capable of causing some very serious harm," Feuerstein said.

Herold said she did not have a problem with Travis in the past. "He didn't have anything but love until this freak accident," she told WNYW.

Pacelle saw it differently. "This is a perfectly predictable outcome of an inherently dangerous situation," he said.

Police in Connecticut say Travis had acted out previously.

The chimp, which was well-known and liked in the community, escaped in 2003 and "wreaked havoc" on the streets of Stamford for a couple of hours, said Stamford Police Capt. Rich Conklin.

Pacelle finds it outrageous that some people raise chimps as pets.

"If the owners are stupid enough to allow this animal into their home, they shouldn't be allowed to jeopardize the rest of the community," he said.

At least 20 states have laws that make owning a primate illegal.

The Humane Society is asking people to support the passing of The Captive Primate Safety Act, which would prohibit interstate and foreign commerce for primates as pets.

Preiss gave three reasons why chimps shouldn't be pets. "One, (they're) too dangerous, two, they can transmit disease," she said, and third, "they belong in the wild."

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