OTTAWA -- The Information Commissioner of Canada has found evidence of "systemic interference" with access to information requests by three Conservative staff members, and suggests bringing in the police.

But the Public Works Department, where the interference occurred, says it won't be referring the matter to the RCMP because police did not lay charges in a similar case.

Suzanne Legault delivered her second report Thursday following an investigation into cases that date back to 2009 in the office of cabinet minister Christian Paradis, who held the Public Works portfolio at the time.

She had already found against one staff member, Sebastien Togneri, in a previous investigation that was sparked by a Canadian Press access-to-information request.

Togneri resigned in 2010 after The Canadian Press reported he had been involved in other cases of meddling. Colleagues Marc Toupin and Jillian Andrews also turned up in emails about withholding information, but they continued to work with Paradis.

Legault looked at more cases, and found that Togneri, Toupin and Andrews interfered in five instances and exerted pressure over bureaucrats.

Andrews currently works as a senior aide in the office of Environment Minister Leona Aglukkaq. It is not clear if Toupin is still in the government's employ.

"Through the investigation that is the subject of this report, I found a pattern of improper involvement by a small group of ministerial staff members at (Public Works) in responding to requests under the Access to Information Act," Legault wrote in her report.

"These staffers inserted themselves in various ways into a process that was designed to be carried out in an objective manner by public servants. Consequently, the rights conferred under the Act were compromised."

Legault also described how she had to resort to a court order, after Paradis' successor at Public Works Rona Ambrose refused to divulge records held within the minister's office.

Ministerial records are not covered by the Access to Information Act, but the Supreme Court has found that they can be reviewed if they deal with departmental matters.

It turned out that those records -- emails between political staffers -- did deal specifically with departmental business. They helped to form Legault's finding against Toupin.

Legault says there is evidence a possible offence has been committed.

The act forbids anyone to "direct, propose, counsel or cause any person" to conceal a record, with a maximum penalty of $10,000 and two years in jail. No one has yet been convicted under the section.

But Legault again noted her dismay that she cannot refer matters to the Attorney General of Canada for investigation herself, since ministerial offices and their staff are not covered by the Act.

In the case of Togneri, former Public Works Minister Rona Ambrose referred the matter to the Mounties, but no charges were ever laid.

Public Works, now under minister Diane Finley, told Legault's office that given no charges were laid in a similar case, "it would not be a prudent use of the RCMP's limited resources to refer these current files to them."

Finley's office did not respond to a request for comment.

The department also undertook to make changes to how it handles access to information after the Togneri report, which Legault said were "laudable initiatives."

She made a pointed reference to the responsibility of ministers and top bureaucrats to make sure the access to information system is protected. She said that a culture of "pleasing the minister's office" had been fostered among public servants.

"The integrity and neutrality of the access system depends on strong leadership from the top," she wrote.

"Ministers and senior managers must ensure their employees know their responsibilities with regard to access to information, and the limitations on their roles."