Former Strathfield councillor Sharangan Maheswaran appeared at the NSW Independent Commission Against Corruption on Tuesday, questioned over allegations he spied on and blackmailed former mayor Matthew Blackmore.
It is expected to be the final day of the inquiry's public hearings, which kicked off in July.
Mr Maheswaran, lawyer for fugitive property developer Jean Nassif, has also been grilled at the inquiry over dealings on Nassif's behalf with NSW Liberal Party operatives.
The operatives - one of which is the brother of former premier Dominic Perrottet - are accused of accepting prohibited donations from Nassif in exchange for political outcomes, including the ousting of a state minister and the building commissioner.
On Tuesday, Mr Maheswaran was asked about an agreement from early 2022 with councillors Mr Blackmore and Karen Pensabene.
It would have had Ms Pensabene take over as mayor before the 2023 election.
Mr Blackmore claimed earlier in evidence that when he pulled out of the agreement, covert material gathered against him - including recordings of his children - was used to force him to stand down.
Mr Maheswaran said he had Mr Blackmore under surveillance by a private investigator intermittently from 2021, prompted by supposed suspicious behaviour from the former mayor, and admitted his vendetta against him grew personal.
"Matthew is getting f***ed sideways," Mr Maheswaran said in a text message to Ms Pensabene, read aloud to the commission.
"I actually don't care if he hands mayor over. He's getting wrecked."
Counsel assisting Peggy Dwyer SC declined to read a following message out.
"That's a derogatory and unfair comment. Do you accept that?" Dr Dwyer asked.
"Oh, I don't accept that," he replied.
However, Mr Maheswaran agreed his "personal dislike" of Mr Blackmore developed to the point he wanted to damage him regardless of the political outcome.
In other messages, the inquiry heard Mr Maheswaran told Ms Pensabene: "We want to menace Matthew".
To Dr Dwyer's disbelief, Mr Maheswaran insisted it was a typo, and meant to say words to the effect of: "We want to not menace Matthew".
"Let me be very clear ... I'm suggesting to you your evidence to this commission in relation to that message being a typographical error is false," Dr Dwyer said.
"I can only tell you what my recollection is today," Mr Maheswaran replied.
The commission also heard Mr Maheswaran briefed popular political YouTuber Jordan Shanks-Markovina, known online as friendlyjordies, against Mr Blackmore.
He admitted this was because he wanted Mr Shanks-Markovina to run a negative story about Mr Blackmore, but insisted it was not related to his wanting him to resign as mayor.
