Commission head John Vertes told the inquiry Thursday that Horne wrote him a letter on Feb. 19 rejecting Vertes's request for an extension on the April 30 deadline to submit his report to the legislature.
Vertes said logistical problems and extra evidence make it impossible for him to submit a full report by then.
"Anyone familiar with the history of commissions of inquiry in Canada — both federal and provincial — knows that requests for an extension of time are not unusual," Vertes said in Calgary after the commission finished calling witnesses.
"To reject such a request is unprecedented.
"Not only is such a rejection unprecedented, it borders on an interference with the independence of this commission, since it would require me to rush through a report that would not be as complete or thorough as I would want."
Vertes said he knew in January that the commission would go overtime and asked Horne on Jan. 22 for a six-month extension.
He said Horne's rejection letter didn't arrive until a month later and did not give reasons for saying no.
Vertes said he could have shut down the hearings at that point and met the April 30 deadline with an "incomplete" report or continued the hearings knowing he'd be late with his summation.
He chose the latter.
"To do otherwise would be a disservice to the people of Alberta," he said.
"They, as well as the participants in this inquiry, deserve a report that is comprehensive, thorough and carefully reasoned."
Vertes said he has asked Horne to reconsider the deadline decision.
In an interview, Horne declined to comment on the reasons for the initial refusal, citing cabinet confidentiality. He said he will take Vertes' latest request back to the table.
"We will carefully consider it," said Horne.
The minister dismissed Vertes' suggestion that the government is interfering with the inquiry's work. Horne said he has been careful not to comment in public on developments at the hearing.
"There is no basis for any allegation there has been interference," Horne said.
In the meantime, Vertes plans to plow ahead with final submissions in early April and hand in his report late by Aug. 31.
In the last three months, the inquiry has heard from 68 witnesses, which has generated 3,000 pages of testimony and 158 exhibits.
Vertes said even with the extension he expects the inquiry will stay within its $10-million budget.
Delays could not have been avoided, he added. There were logistical challenges setting up the public hearings in Edmonton and Calgary. He also said the commission had to deal with new and emerging evidence.
Vertes's comments underscore difficulties his inquiry has encountered because, as he pointed out last month, it does not revolve around a single defined event, but is instead looking for trends.
The task is further complicated because Vertes was mandated to look only for current examples of queue-jumping.
Lawyers for some of the parties have argued that he therefore couldn't look into the past. Commission lawyers have countered that only by exploring past queue-jumping could it be determined whether it was still occurring.
In the end, all parties seem to have informally agree to more or less go as far back as 2008 and 2009, when the province was squeezing all health regions into the Alberta Health Services superboard.
The inquiry was criticized early on as a waste of time as it uncovered isolated cases of random queue-jumping.
But that changed in January when clerks from Calgary's Forzani and MacPhail Colon Cancer Screening Centre came forward to testify to a queue-jumping scheme linked to a private boutique health clinic.
Since then, the inquiry has heard evidence that the Helios Wellness Centre and the publicly funded Forzani clinic both rent space from the University of Calgary.
The founder of Helios, University of Calgary radiology professor Dr. Chen Fong, has testified that Helios patients pay $10,000 a year for yoga, diet, and exercise advice and that, in turn, Helios donates $200,000 or more a year to the university.
The inquiry has also heard testimony that from 2008 to 2012 Dr. Ron Bridges — an associate dean in the university's faculty of medicine and the founder of the Forzani clinic — moved Helios patients to the front of the line at the public centre to be tested for colon cancer in weeks while everyone else waited years.
Bridges has testified he didn't go through normal booking procedures, but denied trying to get Helios patients fast-tracked.
The issue raised larger concerns about the role of private clinics operating alongside the public system and doctors who work simultaneously in both spheres.
Even with the extra testimony, the inquiry has still been accused of ignoring key evidence, including reports that queue-jumping led to needless deaths of lung cancer patients waiting for surgery more than a decade ago.
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