ACT Director of Public Prosecutions Shane Drumgold was questioned for a third day at an independent inquiry into how the territory's justice system handled rape allegations made by Mr Lehrmann's ex-colleague Brittany Higgins.
Mr Drumgold told the inquiry the federal government had been involved in the matter "early" and Ms Higgins was concerned about political interference in the case.
He said he was concerned by "strange events" over the course of the investigation and trial that led him to believe there was a wider interest in the failure of the prosecution.
"Some of the questions in my mind, hypothetically, were: was this a government minister exerting pressure through the federal (police) commissioner onto ACT Policing to make a matter go away," he told the inquiry on Wednesday.
"I felt the plan may have been if (police) can convince me to give them the imprimatur not to charge then a political matter would go away, was my first presumption.
"As time went on I felt that their interests aligned with an unsuccessful prosecution, that was my fear."
Asked if he thought there was a political conspiracy to stop the trial from going ahead, Mr Drumgold said there were "enough incidences to make it possible, if not probable".
Mr Lehrmann denies raping Ms Higgins in Parliament House in 2019.
He faced an ACT Supreme Court trial in October 2022 but juror misconduct meant a verdict was not reached.
Mr Drumgold said there was also "unprecedented pressure" on his office not to proceed with a retrial.
"Police had a passion for this prosecution to fail, that was my observation," he said.
Prosecutors ultimately dropped the charge against Mr Lehrmann due to concerns about the impact of a second trial on Ms Higgins' mental health.
Earlier, Mr Drumgold said he was concerned by a police decision to interview Ms Higgins a second time, something he said was "irregular" in a sexual assault investigation.
"I held concerns because a subsequent interview would be traumatic to a complainant (and) my position was that if there was an inconsistency it should be left to the defence," he said.
"The (police) evidence-in-chief interview looked like a cross-examination. It looked like a defence cross-examination."
Mr Drumgold said he held separate concerns about the motivations of some police officers when communicating with Mr Lehrmann's defence team.
"My concern was (police) going to great lengths to feed inaccurate information, inaccurate assessment of information, in the hope of derailing the case," he said.
Asked whether his assessments of police conduct during the case affected his own ability to be objective, Mr Drumgold said no.
The ACT government established the inquiry after accusations by police and prosecutors about each other's conduct during the case.
Inquiry chair Walter Sofronoff is examining how territory police, prosecutors and a victim support service handled Ms Higgins' allegations.
Officers from ACT Policing and the AFP are expected to give evidence to the inquiry, as well as Mr Lehrmann's defence lawyer and journalist Lisa Wilkinson.
