He said Blowers had suffered the "public humiliation of a significant personal fall from grace" but his late admission of guilt stopped some details embarrassing to police being aired in open court.
A Herald inquiry revealed in September last year that the detective who blew the whistle on Blowers, who was his supervisor, was himself investigated before his concerns were taken seriously.
Andrew Glendinning became suspicious of Blowers' behaviour and tailed him on visits to the home of a woman before handing a dossier - which included covert photographs - to senior management in Northland.
But the actions of Mr Glendinning, not Blowers, were investigated first.
He was removed from the organised crime squad and placed under strict supervision while being subjected to an internal code-of-conduct inquiry.
This centred on his use of the National Intelligence Application computer system, which is meant to be used only on official police business.
After several weeks, he was cleared of any breaches and attention switched to Blowers, who became the subject of an internal inquiry which was later escalated to a criminal investigation.
Mr Glendinning was listed as a trial witness and did not return phone calls.
Yesterday, Superintendent Russell Le Prou, the Northland district commander, said he was unable to discuss details of employment matters involving staff but acknowledged mistakes were made.
"Yes, there were some errors ... We could have done things better at the outset. We've learned some lessons along the way. At the end of the day, we got the right result. We've got rid of a bad apple."
Police lawyers are considering whether an internal report on what happened can be released to the Herald under the Official Information Act.
"We genuinely want to work out the balance between the public interest with our obligations in regards to employment matters and privacy and release what we can."
Mr Le Prou also offered reassurance to any Northland police officer with concerns about a colleague.
"If there is a matter like this which gets reported to me, or my leadership team, we will investigate it appropriately."
The downfall of Blowers, a 21-year police veteran, started because of his affair with an informant, according to Justice Venning.
Blowers had legitimately cultivated her as a source but Justice Venning said the relationship became "inappropriate and intimate".
As far back as 2002, police bosses had told him to cease all contact with the woman, whose identity is suppressed.
"You have lost the home you had built up with your wife and you have suffered the very public humiliation of a significant ... fall from grace."
Blowers had maintained his innocence since his arrest in 2013 but made a shock admission during his High Court trial in October when he pleaded guilty to supplying methamphetamine over a period of 12 months and a charge of stealing the drugs.
The drugs were taken from a seizure of 58g at a motel in October 2011 and testing by the Institute of Environmental Science and Research showed 81 per cent purity. But a second test showed 29 per cent purity, and table salt was present.
"It looked the same, it weighed the same, but it was not the same," prosecutor Phil Hamlin told the court. "Someone had carefully made up the 58g to make it look like the original, but it was not."
Blowers' guilty plea came only after evidence showed he was the only person to have access to the drugs.
He was regularly supplying methamphetamine to his informant for her to sell, normally in 1g amounts, and tipped her off about police inquiries.
Justice Venning said he "constantly pressured her for cash". The largest single sum she paid him was $7000.
Blowers told her who not to associate with in the criminal community so she could avoid being caught up in inquiries.
He claimed he stole the drugs to protect his family from perceived threats and out of fear of the criminal underworld, but Justice Venning dismissed that.
"If you and your family had been genuinely threatened by gangs there were steps the police could, and would, have taken to protect you."
