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."
Dr Spindler said the two-year-old calf had developed at a faster rate than most baby elephants.
"Pathi Harn, we now know, is a very unusual elephant," she said.
"He's developed much more quickly than anyone could have expected.
"It's entirely possible this spike in testosterone contributed to the sudden changes in behaviour we saw that day."
She said it appeared Pathi Harn had no ill will towards his trainer.
"We're not sure if the two females and the spike in testosterone caused him to act that way, but it was out of the ordinary for Pathi Harn and even for elephants his age to have those levels of testosterone."
Most elephants do not display any indications of testosterone until they are four years old, Dr Spindler said.
Tuesday also marks Ms Melo's return to the zoo on a fulltime basis.
She spent 12 days in a Sydney hospital in October after she was pinned to a bollard by Pathi Harn, formerly known as Mr Shuffles, during a routine training exercise.
Ns Melo was conscious when paramedics first arrived, but lapsed into unconsciousness and had a cardiac arrest for about five minutes.
After a spell of convalescence at Sydney's Royal North Shore Hospital, Ms Melo was given the all clear to return home.
While recovering in hospital, she suggested the zoo's review include a blood test that examines Pathi Harn's testosterone.