Constable Lauren Conte was allowed to remain in her job despite being found guilty of illegally accessing the force's confidential database to snoop on an associate of Hells Angels Nomads sergeant-at-arms Paul Peterson.

Constable Conte, who allegedly met Peterson while he was facing serious charges in relation to a violent kidnapping, escaped conviction but was given a 12-month good behaviour bond in 2011 by a Ballarat magistrate, who told her she had ''ruined a promising career''.

But last year a police disciplinary board decided to reinstate the suspended constable in a move understood to have infuriated senior police, including Chief Commissioner Ken Lay.

It is believed Mr Lay sought advice about whether he could intervene in the Conte case but was told he could not.

On Wednesday, Mr Lay confirmed revelations that a policeman with close, long-standing and unapproved ties to Comanchero bikie gang president Amad Malkoun kept his job for years despite being the subject of several internal investigations.

''We didn't have the systems in place … to collect this evidence and actually get this person out of the organisation,'' Mr Lay said of former sergeant Richard Gelemanovic, who resigned four months ago while facing his fourth corruption probe in 10 years.

In 2003, the Australian Federal Police reported to Victoria Police the close association between Mr Gelemanovic and Malkoun, who was convicted of heroin trafficking in 1988 and who took over the Comancheros in 2009. Federal agents investigating Malkoun's suspected drug trafficking in 2003 observed Mr Gelemanovic fly overseas and regularly communicate with the crime boss, prompting the AFP to report its concerns to the Victoria Police Ethical Standards Department and arrange for ESD detectives to conduct surveillance on the pair.

Asked why Mr Gelemanovic had not been disciplined or sacked in 2003, a police spokesman said the ''allegations of a criminal association'' were ''unable to be determined'' by ESD.

Mr Gelemanovic's relationship with members of Malkoun's syndicate was investigated again in 2008 by the state's now disbanded police watchdog, the Office of Police Integrity. But it is understood that the OPI shelved its inquiry in early 2009 after incorrectly assessing that Mr Gelemanovic would not return to work from sick leave.

In 2011, the OPI discovered that Mr Gelemanovic was still working as a policeman after receiving a complaint from another policing agency about the sergeant's continuing association with Malkoun.

Between 2003 and 2012, Malkoun's syndicate was tipped off twice that it was the subject of investigations by secret, multi-agency police drug taskforces, compromising both investigations.

The OPI launched another inquiry into Mr Gelemanovic in 2011 but could not find evidence he was responsible for either leak. But the inquiry confirmed Malkoun's ongoing association with Mr Gelemanovic, who resigned last November, citing ill health and while still under internal investigation.

The OPI probe was run by its tactical investigation unit, which uncovered links between a small number of serving and former police officers and bikie figures.

A Fairfax Media investigation can also reveal that the unit was shut down mid-inquiry last year, sparking serious divisions inside the OPI over claims the agency had prematurely ended the probe.

Constable Conte was found guilty in the Ballarat Magistrates Court in 2011 for inappropriately accessing the police database in connection to her relationship with Peterson. The relationship included regular, unapproved contact and is suspected to have begun in 2007, when the bikie - a known crime figure - was reporting on bail to Constable Conte's station.

Magistrate Michelle Hodgson found Constable Conte guilty of one count of improperly accessing the force database and said she had ruined her career but that, outside of her offending, she was ''an outstanding citizen''.

A police spokesman said in a statement that during a subsequent internal police hearing in May, Constable Conte pleaded guilty to three disciplinary charges and was placed on a 12 month good behaviour bond, shifted to a new station and was denied promotion before May 2014.