Australian Federal Police did not interview Sydney Lord Mayor Clover Moore during an investigation into doctored documents Energy Minister Angus Taylor used to attack her.
AFP Commissioner Reece Kershaw confirmed that Ms Moore was not spoken to before his officers abandoned their investigation into the falsified travel figures.
"The mayor was not interviewed," Mr Kershaw told a Senate estimates hearing on Monday.
Labor senator Kristina Keneally repeatedly questioned why Ms Moore was not interviewed before the AFP decided the allegations presented a "low level of ongoing harm".
"The lord mayor is the victim, if you will, in this circumstance," Senator Keneally said.
"How do you make a determination of harm and a decision not to continue an investigation without speaking to the victim of the alleged crime?"
Mr Kershaw said the decision was objective and considered.
"That's a matter again for the decision-makers and they have made that decision on the materials available to them at the time," he said.
"That was what was referred to us by the NSW Police."
Greens senator Nick McKim asked whether the AFP had considered ringing Mr Taylor to ask whether he had forged the City of Sydney travel figures.
"Isn't that the first thing you'd do?" Senator McKim said.
Mr Kershaw laughed off the question.
"No, we don't operate like that," the commissioner said.
Senator McKim said the failure to interview Mr Taylor was "Alice in Wonderland stuff".
"I can't help but think there's a protection racket being run for Mr Taylor's behalf here," he said.
Cabinet minister Marise Payne encouraged the senator to reflect on his remarks.
"Well, I have thought very carefully, and I stand by my comments," Senator McKim said, insisting he was not reflecting on the AFP.
Mr Taylor sent a letter to the lord mayor last year accusing her of driving up carbon emissions by spending more than $15 million on domestic and international travel for council staff.
But that figure, cited in documents distributed by the minister's office, proved to be wildly incorrect.
Mr Taylor apologised but has never explained where the dodgy document came from.
The AFP abandoned its investigation after determining there was no evidence to indicate the minister was involved in falsifying the information.
The force said the low level of harm and his apology, along with the resources required for the investigation, were also factored into the decision not to pursue the matter.