Giving evidence in his own defence, the lawyer denied deliberately grabbing her but conceded he may have accidentally struck her backside as he walked by.
The lawyer still has interim name suppression which means some aspects of the evidence, such as the location, cannot be reported without potentially identifying him or the complainant.
In his decision released this week, Judge Snell said the woman was a sincere and honest witness but her memory of events was "utterly unreliable".
The squeeze was for "five or six seconds", the complainant said in giving evidence at the trial, although she later conceded any contact must have been only "fleeting".
This was because security camera footage and the evidence of another lawyer, who came forward as a witness, showed any contact as lasting one second at the most.
When questioned in court about the conflicting evidence, the complainant was adamant she was groped.
"There was enough time for me to feel his hand and his fingers totally squeeze my butt."
However, this was rejected by Judge Snell, who said the woman's evidence as to the nature and duration of her allegation changed over time.
He pointed to the evidence of the witness lawyer, who approached the complainant a week after the incident to say he thought something "improper" happened the last time he was in court.
In his statement to the police, the lawyer said the woman told him she "thought she felt something", describing it as a "cup as opposed to a slap".
In giving evidence, the woman denied making those comments to the lawyer.
But Judge Snell said the lawyer was a "careful and considered" witness, whose statement to the police shortly after the incident would be a more accurate account of events than the complainant's evidence a year later.
"It is clear, as was elicited in the cross-examination, that she became emotionally involved with the allegation once she had decided the action was deliberate and indecent. I suspect that over time the allegation has increased in terms of seriousness and duration in her memory," said Judge Snell.
"I make it clear that I do not think that she is a dishonest witness, but simply an unreliable witness who, over the passage of time, has built on the allegation from what it was originally."
In his findings of fact, Judge Snell wrote the complainant felt a "fleeting" touch to her bottom area and turned to see the lawyer as the only person in the vicinity.
When she viewed the CCTV footage, that was unclear as to what happened, the complainant felt it may have been more a "cup" than an accidental touching.
The judge said her reaction when the lawyer witness approached her the following week, was confirmation that up until that point she was not entirely sure of what happened.
What cannot be overlooked, wrote Judge Snell, was the lawyer who came forward as a witness to say the alleged contact did not seem to be accidental.
In his evidence at the trial, the experienced litigator said he saw the other lawyer walking towards him and deliberately reach out to "strike" the woman's bottom, then take his hand away.
"I recall her looking surprised and looking around," said the lawyer. "[The defendant] walked by as if nothing unusual had happened, nonchalantly."
The witness said the "bizarre" incident made him uncomfortable but he wasn't sure what to do.
In Judge Snell's findings, the lawyer's lack of reaction was equally as important as his observation the contact seemed deliberate.
"It is clear that [the witness's] evidence is that [the accused lawyer] seemed to behave as if nothing at all had actually happened, which is entirely consistent with somebody accidentally touching someone as they reach back while walking, talking and negotiating a path to the door," said Judge Snell.
"I find that, while the action of [the accused lawyer's] arm going backwards and having contact with a striking motion with the buttock area of the complainant may have seemed like a deliberate action, I cannot rule out the possibility that it was an accidental motion."
The judge also said it was very unlikely the accused lawyer would deliberately grab someone in such a public place, given the consequences to his reputation and career if he was caught.
The complainant told the Herald on Sunday she was disappointed but not surprised at the not guilty verdict.
"That in itself is sad."
She said the justice system process for complainants of sexual crimes was "brutal, cruel and unforgiving", but she had no regrets in speaking up.
"This sickness must not be ignored and swept under the carpet. There must be a clear message, that this will not be tolerated, which is then supported with action."
