There will be no prosecutions of anyone following damage to the Marsden Point fuel line which led to fuel shortages at Auckland Airport last year.
The Northland Regional Council says it cannot find enough evidence to lay charges and "does not have a case for prosecution of any party".
In September, the pipeline between the Northland refinery and Auckland ruptured at Ruakaka - shutting the line and forcing airlines to ration fuel at Auckland Airport, which led to flight cancellations.
Council group manager Colin Dall says they found an unknown digger illegally searching for swamp kauri "may" have operated around the pipeline.
The actual date and cause of the damage were not known. It could have happened any time after the pipeline's last inspection in July, 2014.
The land owner said that year he had been approached by a contractor asking for permission to "scratch around and see if there were any [kauri] logs".
He gave the unknown contractor "limited permission", pointing out the pipeline.
Mr Dall said the owner could establish he had taken "all reasonable steps" to prevent an offence and there were also warning signs at the site.
Transport invoices led to a job where a digger was delivered to the property in August.
They spoke to two digger drivers. One said he could not recall doing any work at Ruakaka. The other said he been at the site for one day - but not around the pipeline.
There was no legally credible evidence the digger involved had operated around the pipeline itself, or that either of the two digger drivers had worked that pipeline area, Mr Dall said.
Legal advice was the evidence was well short of the beyond reasonable doubt standard of proof.
Meanwhile, the council will also not take any action against Refining NZ over the discharge of about 124 cubic metres of jet fuel.
"In a nutshell, the discharge was beyond the control of either party or their employees."
Mr Dall said the council's investigation was now effectively at an end.