That's according to a source close to the investigation, who spoke on the condition of anonymity Tuesday -- one day after a 29-year-old woman from the United States was killed on a safari outside Johannesburg.
A family member identified the victim as Katherine Chappell of Rye, New York. Jennifer Chappell declined to speak further Tuesday night.
The victim was taking pictures and likely didn't see the lion approach from the side, the source said. She was a passenger in a vehicle with a tour operator when the lion attacked.
The operator was hurt trying to fight off the animal, but he is expected to survive, according to Scott Simpson, assistant operations manager at Lion Park.
Lion Park said witnesses confirmed that the passenger's and driver's windows were open.
The lion stopped about a meter from the vehicle as the woman continued taking pictures, a Lion Park statement said. The lion then lunged at the car, biting the woman through the open window.
Camp staff chased the lion away, the statement said.
An ambulance arrived in minutes as the staff rendered first aid. Chappell died at the scene.
Simpson said the lion would be taken to a second property while the park investigates. It will not be euthanized.
The park has had incidents before, all stemming from open windows, he said.
"That's absolutely forbidden at our park," Simpson said. "There are numerous signs, and we hand out slips of paper to all guests warning them to keep their windows closed."
The notice warning guests to keep their windows closed was found on the passenger side seat of the vehicle of the woman who was killed, the source close to the investigation said.
Lion Park, a wildlife center in South Africa's Gauteng province, boasts a variety of animals, including lions, zebras, giraffes and wild dogs.
"It is incredibly sad that a life had to be lost in this manner," the Lion Park statement said. "Visitors to South Africa need to remember that predators are dangerous and rules are there for their own safety. If all the rules are adhered to (during) your visit to the Lion Park, national parks and other similar facilities will be a safe and treasured experience."