Police have since said Mehrtens' arrest was unrelated to the homicide investigation.
Defence barrister Peter Kaye said Mehrtens maintained "that at no stage was he involved" in manufacturing methamphetamine.
"Clearly he has to accept he must be sentenced on the jury's verdict," Mr Kaye said.
Mr Kaye said Mehrtens claimed he travelled between Auckland and the Coromandel Peninsula acting as a courier of pseudoephedrine, the prescription drug used to make P.
Justice Keane rejected that, finding that Mehrtens was involved with large-scale production and obtained enough pseudoephedrine to produce more than 2kg of methamphetamine and "more likely" 3-4kg of the illicit drug.
The street value of P can be up to $1m a kilogram.
Mr Kaye said Mehrtens' criminal history only had relevant convictions from 1990, when he was sentenced for "minor cannabis consumption".
"[Mehrtens is] before you at the age of 57 and obviously he's in for a lengthy sentence, which at that age is going to mean that really for most of the useful period of his life he's going to be incarcerated. And that of course is a sobering thought," Mr Kaye said.
He said Mehrtens had four daughters and a son, all of adult age.
In a pre-sentence report for the court, Mehrtens admitted he had an addiction to methamphetamine and used at least 1g a day, sometimes more.
He said he used it "usually just to get a bit of a buzz".
The jury found Mehrtens guilty of eight offences, including large-scale manufacture of methamphetamine, conspiracy to continue manufacturing the drug, possession of the drug for supply and the actual supply of the drug.
The Crown case was that Mehrtens and Filer were involved in the manufacturing, either as cooks or close company of the cooks.
Justice Keane set no minimum sentence period but said Mehrtens would need to undergo programs in prison to address his drug dependence before the Parole Board would consider releasing him.
The pre-sentence report said Mehrtens would remain a "high risk" of reoffending unless he faced his drug addiction.
In sentencing Mehrtens to 17 years and nine months imprisonment, Justice Keane also ordered concurrent sentences of five years each for possession and conspiracy charges, three years for possession to supply, and two years each for counts of supplying.
Mehrtens was supported in court by family, who blew kisses to him as he was taken into custody.
Filer's appeal against his conviction was dismissed by the Court of Appeal last month. He withdrew his appeal against a sentence of 17 years imprisonment.
