"In each of those cases police have brought them to the courts, and the public can be assured that when police get any hint that someone is involved in illicit activities they will be investigated, and as seen in these cases, arrested and put through the court," he said.
Mr O'Connor said while "one is too many", it was not a sign of a corrupt police service but a healthy one, saying it would be worse if such cases weren't being brought before the courts.
However, he tried to downplay the role Mr Thomson held within the police, saying: "He wasn't a police officer he was a lawyer employed by police; that's key to remember.
"Had he not been working for police he may well have been able to carry on with his activities and not ended up in court, so the police are far more vigilant in this than most [other employers]."
He moved to assure the public that the police are not afraid of to prosecute one of their own.
"As any of the lawyers who work with police officers will tell you, police are extremely vigorous and rigorous whenever they come across anything that may be criminal behaviour by any member of the police," he said.
In May this year Auckland prosecutor Tim Sarah was sentenced to four years' jail after pleading guilty to five charges, including supplying methamphetamine and dishonestly accessing the police intelligence computer system to get confidential information.
Sarah, 37, sold methamphetamine during his lunch break and passed secret information from police files to his drug dealer.
In May, 36-year-old Henderson policeman Peter Pakau was arrested on 27 counts relating to methamphetamine and accessing the police computer system to supply information to gang members.
Last month, Pakau's colleague Lotovale Perese, who worked as police prisoner escort at the Waitakere District Court, pleaded guilty to smuggling pre-ordered cannabis, letters, lighters, tattoo ink, USB sticks, a cellphone, a watch and various other contraband to 16 prisoners over a six-month period. The 42-year-old will be sentenced in December.
Earlier this year former Whangarei Detective Sergeant Michael David Blowers was charged with supplying methamphetamine and selling cannabis while in charge of the organised crime unit in Northland.