Too much power inside the Premier's Office led to the "train wreck" this year during property tax season, when thousands of New Brunswickers were assessed and billed too much, Green Party Leader David Coon says.

"All New Brunswickers have to ask why is the chief of staff of the premier so involved in fundamental questions around policy — in departments and Crown corporations — rather than cabinet ministers?" Coon said in an interview on Information Morning Fredericton.

"You can't possibly run a government out of the Premier's Office."

In a report this week, Auditor General Kim MacPherson said her office could not get to the bottom of who pushed for rushing a new property assessment system into service two years ahead of schedule. As a result of the rush, Service New Brunswick made thousands of assessment errors.

- Auditor general blames Service NB for rush to bungled tax assessment system

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MacPherson blamed the leadership of Service New Brunswick for failing to acknowledge the "high risk" of "fast-tracking" the new system.

Although she couldn't identify a specific spark, or person, behind the fast-tracking, MacPherson offered a short list of suspects: former Service New Brunswick CEO Gordon Gilman, who retired before the auditor general's report came out, and Premier Brian Gallant's chief of staff, Jordan O'Brien, who called Gilman after a presentation on the aerial assessment technology.

Coon said the fast-tracking of the system by Service New Brunswick was the consequence of trying to govern out of the Premier's Office. He cited Gilman's decision to hire people to implement the accelerated system before getting approval from the Crown corporation's board.

"You've got deputy ministers or CEOs of Crown corporations interacting with [the Premier's Office] on a regular basis, rather than working through ministers or their board of directors."

Gallant has not accepted any responsibility for what went wrong with the property bills last spring and blamed civil servants right away, but his denial has also been a flag for critics.

"If the chief of staff is involved, the chief of staff is speaking for the premier, that is the point," said Progressive Conservative Leader Blaine Higgs said on Information Morning.

"If the premier's chief of staff is doing things the premier is unaware of, that is a major problem. The chief of staff is the premier's voice inside of government."

A slide-show presentation obtained by CBC News earlier this year said the new system would take three years to implement, but after the May 6, 2016, presentation to Gallant, Service New Brunswick was told, "I want to see it in half that time," a comment attributed to the premier.

MacPherson has called that comment in the slide show "fictional."

"We did not have any direct link that the premier directed this to happen but it was the events of May 6 — by the end of the day the wheels were in emotion to reduce the timelines by two years," she said Friday. "And it started that day with a presentation to the premier on aerial photography."

Emails showed Service New Brunswick CEO Gordon Gilman asked staff to accelerate implementation after the presentation.

"Everyone within property assessment services truly believed that the premier directed this to happen," MacPherson said. "No one talked with the premier."

She said the political consequences of the tax scandal aren't her territory.

"When people go to vote, that's when they will make their decision. My job is to present to the legislature the results of our work."

Who's to blame?

Although both Coon and Higgs applauded MacPherson for her report on the scandal, they still want a better picture of its genesis.

"Why did no one pull the brakes at any stage there to avoid this fiasco?" Coon asked. "Right now we're still lacking information in terms of how it all began."

Higgs said it's been suggested that Gilman, O'Brien and René Landry, director of modernization at Service New Brunswick, be called under oath to answer questions from a legislative committee.

"Putting them under oath will get to the bottom of the real information and the real facts," he said.

Coon said he doesn't think this is the end of the property assessment affair, but he hopes changes are implemented so it doesn't happen again.

"We do need to eliminate this whole business of governing from the Premier's Office because we're going to continue to have other train wrecks," said Coon.