American's chimp attackers will be allowed to live Updated at 9:51 a.m. (AP) JOHANNESBURG - Two adult chimpanzees that viciously attacked a U.S. student at a primate sanctuary in South Africa were defending their territory and will be allowed to live, the lead government investigator said Tuesday. Conservationist Dries Pienaar blamed human error for Thursday's attack. But one of the sanctuary managers, Eugene Cussons, said he did not blame Andrew F. Oberle for crossing between two safety fences to retrieve a rock that the chimps were in the habit of throwing at tourists. Oberle was in critical condition and in a medically induced coma in the hospital by Monday night. On Tuesday, doctors refused to describe his condition saying the family, who had arrived from the United States, is asking for privacy. American chimp attack victim improves in Africa American critical after chimp attack in S. Africa Pienaar told The Associated Press that the chimps tore some fingers off one of Oberle's hands, among other injuries. This was "to my astonishment, I couldn't believe it because I know those chimps personally," he said. He said he found no negligence on the part of the Jane Goodall Institute's Chimpanzee Eden SA in eastern South Africa. "The only thing that happened is Andrew stepped over the small barrier fence and went right up to the electric fence," he said. We all know that they are tame chimps, but he shouldn't have done that, he's a researcher, he's supposed to read the body language. Oberle was leading a group of tourists at the time. The visitors were 33 feet from the second fence, as required by safety rules. After Oberle stepped over the first fence, the chimps dragged him under the electric fence and mauled him around the head and arm. Cussons said he was happy that Pienaar's investigation found the chimps were involved in territorial defense and would not therefore be killed or punished. He said he was forced to shoot one of the chimps, but not mortally, after he and a ranger failed to scare the animals into releasing Oberle, even when they drove a car at them. Chimp Nikki, aged about 16, was injured in the abdomen and is being treated at the Johannesburg Zoo. The other attacker, Amadeus, in its 20s, is on lockdown with his family at the sanctuary. Pienaar, who has worked as a conservationist for 33 years, said he condoned the shooting, a last option under protocols that recommend first shock treatment or pepper sprays. "Other than that I'm happy with things," Pienaar said. I'm not having the chimps put down. I don't think there's reason for that. Oberle knew primate research was not without risks. But after having volunteered at Chimpanzee Eden in the past, he was eager to pursue graduate research with abused and orphaned chimpanzees. He knew the people, the chimps, and it was a good opportunity. "We all really encouraged him," said Lisa Corewyn, a primatology doctoral student at the University of Texas at San Antonio where Oberle is working on his master's degree. Once we knew he wanted to work with chimps, we said 'Go for it!' Oberle, 26, had been passionate about chimps since the seventh grade, when he saw a film about Goodall, said his mother, who spoke to The Associated Press before leaving Missouri for South Africa. Goodall, a famed primatologist, discovered that chimps were the first non-human animals to make and use tools, an area of research that also intrigued Oberle. Before enrolling his master's program, he worked for several years as a camp counselor at the St. Louis Zoo, where he also did primate research, zoo spokeswoman Susan Gallagher said. "He was enthusiastic, engaging and made children understand the need for conservation," Gallagher said. He is very well-liked and respected at the zoo. Corewyn, who met Oberle in 2008 or so when he was taking an undergraduate anthropology class she was teaching, also described him as positive and enthusiastic, particularly about the graduate program he eventually applied to. The program is unusual, she said, in that it has three primatologists in its anthropology department and a large contingent of primatology graduate students doing research around the world. Oberle stood out in the group because his background was with captive animals, while most of his peers study primates in the wild, Corewyn said. He made an extended visit to the Goodall institute a year or so ago to observe the chimps and then returned last month for a follow-up visit, Cussons said. He had training to ensure he understood how chimpanzees might behave in captivity and knew to keep a safe distance. He also received additional training before speaking to the tour group. "Chimps are notoriously difficult to work with, we all know that," said Corewyn, whose own research is with howler monkeys. But people that love chimps, love their chimps. Male chimps can stand up to 5 feet, 7 inches tall and weigh about 154 pounds, according to the Goodall institute. The sanctuary's website did not say how large the two that attacked Oberle were.