The silverback gorilla whose escape sparked a lockdown at ZSL London Zoo managed to drink more than five times his daily ration of blackcurrant squash before he was captured, a zoo chief has said.
Professor David Field, the ZSL's zoological director, said Kumbuka raided his food store after exiting his enclosure through two security doors that had been left unlocked by a keeper as he was feeding the female gorillas.
The "alpha male" was kept calm by the member of staff, with whom he had a "close bond", before guzzling five litres of undiluted sugar-free squash and eventually being tranquillised and moved back to safety, an in-house investigation into the incident said.
Armed police were called to the central London attraction and visitors were evacuated when the alarm was raised following the ape's bid for freedom shortly after 5pm on October 13.
Professor Field said the experienced keeper had made a "mistake" but his response in calming the animal down should be "applauded".
He said: "As he went down to feed the females, Kumbuka had opportunistically gone through the open door that the keeper had left unlocked and he came out, he just pottered out and started to explore the environment.
"The keeper reacted in a very professional, very calm manner and all his training kicked in, all his animal sense kicked in.
"The bond between Kumbuka and his keepers is exceptional and they talk to each other much as I'm doing to you but it's more 'hey Buki, how are you doing? Everything's fine today, what's happened? Did you see the Trump-Clinton debate?"
Once the keeper had backed behind a safety door and sparked the security alert, the 29-stone Kumbuka went in search of the drink.
"So as the keeper had backed out behind the security door, Kumbuka carried on just exploring the environment, he ventured in, probably knowingly, to where the food store is kept next to his den, in the keepers' area, and helped himself to some blackcurrant squash.
"He certainly enjoys it but alongside that he enjoys fruit teas and other flavours as well but the blackcurrant squash was what was available.
"He's a big boy, 29st, so he can cope with five litres but normally it's diluted and rationed. He would probably get about a litre of diluted squash per day. He didn't get his evening fruit tea."
The police were called as part of a full security response because of the risk the animal posed.
"There was a small, small chance because a security door had not been secured that Kumbuka could have got out further than he did so until he was absolutely secure we had to enact our full procedures," Professor Field said.
But despite the animal's security breach, Professor Field said the whole affair was "less dramatic than some would have you believe".
An investigation by Westmister City Council, as the zoo's licensing authority, was "ongoing" and ZSL would be "very open and transparent" with its own findings.
He added: "We are working closely with our licensing authorities to really investigate the root cause of this. It was a really unusual set of circumstances, a really unusual mistake from a highly experience individual. We will look into the reasons why.
"Fundamentally the enclosure that we have is safe, it is fit for purpose."
He added that the human error which facilitated the escape was rare and the risk of mechanical failure meant having an automated security system posed a "greater" threat.