Smith's exact involvement — and greatest sin — has now been revealed by veteran Aussie cricket commentator Jim Maxwell.
The voice of ABC Grandstand claims Smith was simply "stupid enough" to give Warner the benefit of the doubt.
"He (Warner) was the instigator," Maxwell told BC Radio.
"He was sitting in the dressing room with Bancroft and they came up with this ruse. As I understand it, Steve looked over to them and said, 'What are you blokes up to? Oh, I don't want to know'. He went out onto the field and he probably should have been more vigilant, as I said."
Maxwell claimed the entire situation is the consequence of the former 28-year-old skipper's failure to control his 31-year-old deputy.
He said the pair's relationship developed a dangerous stalemate where the so-called attack dog of Aussie cricket considered himself exempt from Smith's supervision — as the more senior member of the two.
"There's been a bit of a history here with Warner and Smith with Warner coveting the captaincy and getting some boy scout honours recently in the T20 (series) in New Zealand and now it's sort of blown up over a period of some incidents here because Warner, as far as I can see, has lost the plot and that's why we got what we got," Maxwell said.
"I worry about Steve Smith's mental state because he's been called everything under the sun as a result of what Warner has really perpetrated here and unfortunately for Steve he was stupid enough, I suppose, to fall in with what was going on without being more vigilant and stopping it before it started."
It comes as Fairfax Media reported Warner was the only member of the dressing room who Smith had no control over.
"Unlike the rest of his team, Smith did not have the personal authority over Warner," the report states.
"Warner was nearly three years his senior with a record that until only recently rivalled Smith's. Managing players was not his strongest suit, leading from the front through weight of runs was.
"An angry Warner had its benefits heading into an Ashes summer, one finished with a marquee series in South Africa. It gave his team the presence and aggression that was missing the last time he had faced the Proteas, though it's hard to see how blood and bile could have averted any of Australia's spectacular batting collapses."
It comes as Aussie Test great Gavin Robertson on Tuesday night claimed Cricket Australia is privately concerned about the lack of control it has on its star players.
He said cricket's governing body in Australia doesn't want it known that the international Twenty20 cricket circuit, headlined by the Indian Premier League, means players can leave the Cricket Australia system and still earn a rich living as a professional cricketer.
"No one will talk about this," Robertson told Fox Sports News.
"Cricket Australia will be saying, 'Shut up Gavin'. They don't want to admit it because they don't know if they control their player. They look at Warner and Smith easily in the top five, the top 10 players in the world. They will adhere to a lot of things because they don't want to lose them.
"They know any player can walk. If David Warner is outed from test cricket for ever and from Australian cricket for ever he'll earn more money in the next eight years on the world stage anyway. We don't have that power any more."
