It does look possible doesn't it? Actually it must have been only a few days before the accident as I have just googled it and viewed a photograph (the same one as in Oliver Graham-Jones's first book I think) dated 6th September 1967. I remember my parents telling me it had been on the news that Diksie had died.
I cannot recall whether or not the accident happened during opening hours; however if it did, there is the distinct and unfortunate possibility that someone somewhere either got images of it happening, or images of the direct aftermath.
Certainly people photographed and videoed the death of the polar bear Knut at Zoo Berlin a few years ago; and equally although no photographs have made their way online to my knowledge, there *must* be dozens if not hundreds of photographs of the deceased female Giant Panda at the same collection taken prior to her death being realised.
The accident definitely occurred during opening hours; it arose when "Diksie" overbalanced (probably nudged by another elephant) whilst reaching out to get some food offered by a visitor.
All feeding by the public was banned shortly afterwards.
This tragic incident did happen during opening hours, my infants school teacher was there when it happened. I remember Dicksie used to come out with her keeper and the public were allowed to give her tit bits, also coins that went into the keeper's pocket. Dicksi's death was well reported in the national press, I can still remember seeing it, I was devastated.
I thinking it was probably on this visit (I was five at the time) that I fed fruit pastilles to the elephants, although from memory that was in a position a bit further to the right than this, so I was contributing to the problem. As a lover of elephants I was always afraid one would fall into a moat in front of me, especially where there was little, if any, "wall" at the top of the moat (it was worse than this inside the house with the addition of a hard floor, and the balancing act I once saw Lakshmi (my 1974 guide book spells it "Lakhsmi") perform had me wanting to leave before she fell; the moat in the house built at Flamingo Park in the late 1960s had a similar lack of a wall and a drop on to concrete, although that didn't stop me and other visitors from feeding hay from bales in the public area to Hannibal and the other elephants on a memorable day in 1971).