Richard Ninness continued his evidence on Wednesday at the Eastman inquiry, which was ordered after fresh doubt was raised about the former Treasury official's conviction for gunning down assistant federal police commissioner Colin Stanley Winchester in a neighbour's driveway in 1989.

Mr Ninness, former commander of Operation Peat, was questioned over the prolonged surveillance of Eastman by his men.

He said he did not believe the years of surveillance - which started three days after the murder - drove Eastman mad.

Mr Ninness also denied police ever harassed the suspect, or that they were trying to provoke him into doing something.

The experienced detective was questioned over the appropriateness of an interview that occurred following their arrest of Eastman for a separate charge.

Eastman had been arrested after a confrontation with a surveillance officer outside the office of his solicitor, Eunice Ryan.

He was charged with an assault for allegedly throwing stones at the officer, and was taken back to City Police Station.

The suspect had previously written to police making it clear that he did not want to be interviewed over the Winchester murder, as was his right, and directed any communication go through his solicitor.

But one of the senior Operation Peat detectives, Detective Sergeant Thomas McQuillen, used the arrest to interrogate Eastman over the Winchester murder while his lawyer was not present. Not a single question was asked about the alleged assault for which Eastman was in custody.

Acting Justice Brian Martin asked Mr Ninness on Wednesday whether he thought his sergeant's actions were inappropriate.

Mr Ninness replied that his detective had ''seized an opportunity''.

He said he always wanted to interview Eastman, saying the suspect might have been able to exonerate himself.

Under further questioning, Mr Ninness then said he had hoped Eastman might confess in an interview.

Eastman's counsel, Mark Griffin, SC, referred the head detective to a letter he had written to a law firm representing the suspect.

In the letter, Mr Ninness said police would be forced to deploy ''other methods'' to investigate Eastman because he refused to co-operate and participate in an interview.

''Unfortunately through lack of co-operation on your client's part, we anticipate a long and protracted police investigation no matter what the outcome of the current inquest being conducted by the coroner,'' Mr Ninness wrote to Eastman's lawyers.

Mr Griffin asked the former Operation Peat head whether that was a threat.

Mr Ninness replied that it was an ''informative letter''.

Earlier on Wednesday, Mr Ninness was referred to the evidence of Ms Ryan, one-time solicitor for Eastman, who said she remembers he was ''extremely upset'' by the constant police harassment and wished it would stop.

Eastman would often come and visit Ms Ryan at her office in Civic during the period around the inquest into Mr Winchester's death.

Ms Ryan recalls seeing plain-clothes policemen outside her office window conducting surveillance.

''They would remain very close to David Eastman when he was coming and going,'' she said in an affidavit.

''In my opinion, they were invading his personal space and harassing him.''

Mr Ninness was asked on Wednesday how he would explain that behaviour, if it actually occurred as Ms Ryan remembered.

''That would be contrary to my instructions,'' Mr Ninness said.

He said there were no specific plans for police to follow Eastman to his solicitor's office, but said surveillance teams were told to follow the suspect generally.

The inquiry continues on Thursday.