An investigation into former Alberta premier Alison Redford's use of government airplanes has been closed by the RCMP, and no charges will be laid.

The Mounties made the announcement in a news release Friday afternoon about the probe that began after allegations were made about Redford in the 2014 Alberta auditor general's report.

In a written statement Redford thanked the RCMP for its investigation "that leaves no lingering questions. 

"I am grateful this is now over," she said. "I was never concerned about the outcome."

The RCMP opened an investigation in April after CBC News revealed Redford had flown her daughter on 50 government flights, including for two holiday long weekends in Jasper.

Soon after, Auditor General Merwan Saher announced he would conduct an audit of Redford's travel expenses and her use of government planes.

On July 29, CBC News obtained a leaked copy of part of his report in which he concluded Redford had derived a "personal benefit" from her daughter's flights.

But his report also unveiled an arrangement in which Redford's staff "block booked" false passengers on government planes so the premier could travel with a chosen entourage. Both Redford and her former chief of staff told auditors they had no knowledge of the false bookings.

Internal government documents show that on the same day CBC News revealed the findings of Saher's leaked report, then interim premier Dave Hancock asked Alberta Justice for a legal opinion.

A special prosecutor subsequently concluded the report's allegations against Redford, if proven by the RCMP, "could constitute the criminal offence of forgery, uttering a forged document, fraud and breach of trust by a public officer."

'File is now concluded,' RCMP say

Last August, the government of Alberta asked the RCMP to review the report and conduct any investigations police deemed appropriate.

Investigators reviewed the report and conducted followup interviews as is their standard practice, RCMP said. 

"In the interest of thoroughness, the RCMP interviewed a wide range of individuals who provided us with information related to the auditor general's report," the force's Assistant Commissioner Marlin Degrand said in the news release.

"We thank them for their co-operation, and the file is now concluded."

The RCMP said it has advised the government and Redford of the findings.

The Opposition Wildrose Party said that although no charges were laid, Redford violated the public's trust.   

"We call on all PC MLAs who participated in the partisan use of aircraft to pay back taxpayers for their involvement," said member of the legislature Drew Barnes.

Redford resigned as premier on March 23, 2014, amid growing controversy over her spending on travel, her use of government airplanes and her leadership style.

She resigned as a member of the legislative assembly for the riding of Calgary-Elbow on Aug. 6, two days after Alberta Justice obtained a legal opinion that criminal charges against her were possible.