A spike in testosterone and two female elephants on heat are the likely reason a baby elephant pinned its trainer against a pole, says Taronga Zoo.
The findings of an investigation into the elephant attack which nearly crushed zoo keeper Lucy Melo to death last October were made public on Tuesday.
Acting general manager of research and conservation, Dr Rebecca Spindler, said neither the zoo or the trainer or the elephant calf Pathi Harn had been at fault.
"We've confirmed two of our female elephants were coming into estrus at roughly the same time," Dr Spindler told reporters at the zoo.
"More surprising is that when we examined Pathi Harn's testosterone, he went through a spike in testosterone that day that was higher than any of our males, including our adult male."