Up to seven years of emails that former ExxonMobil CEO Rex Tillerson wrote under the alias "Wayne Tracker" may have been erased, a company witness has told investigators for the New York attorney general.

The gap is far longer than the three months Exxon initially reported.

The disclosure came from Connie Feinstein, Exxon's information technology security and consulting manager, who was questioned about Tillerson's secret email alias, created in 2007.

During a daylong question-and-answer session related to the attorney general's investigation into whether Exxon mislead investors about climate change, Feinstein explained under oath both how a computer program allowed for the scrubbing of Tillerson's Wayne Tracker emails and the considerable effort the company put in trying to recover them.

A 301-page transcript of the April interview became public last week as part of a batch of documents released by New York Attorney General Eric Schneiderman's office. He lodged them in a state court in support of his claim that Exxon's climate accounting was a "sham" under Tillerson, who is now the U.S. secretary of state.

Feinstein said that a program designed to automatically erase emails from the account's queues after 13 months had never been disabled on the Wayne Tracker account. That opened the possibility that an unknown number of emails may have been erased as far back as 2007.

The Wayne Tracker account was set up without a direct link to Tillerson on Exxon's email servers, giving him a layer of anonymity where he and top executives could address the company's most sensitive business matters, Feinstein said.

ExxonMobil defended itself in court documents Friday against Schneiderman's claims that the company used two sets of books in evaluating climate risk, one set of numbers for describing the risks to investors and the other for business decisions.

The company had "truthfully and consistently" told the public that it "addresses potential impacts of future climate-related policies." Its lawyers also accused Schneiderman of playing to the media and of disclosing confidential and proprietary records that were attached as exhibits to his brief filed last week in New York Supreme Court.

Schneiderman has been investigating the company for years, with the first subpoena issued in the fall of 2015, shortly after InsideClimate News and later the Los Angeles Times published separate accounts of Exxon's knowledge of climate risks since the late 1970s.

Although neither a company spokesman nor Feinstein responded to requests for comment, Exxon has defended the Wayne Tracker emails as "entirely proper" and said there was no attempt by the company to conceal them from investigators.

However, Schneiderman has said the existence of the account was never reported to his investigators, as it should have been under the subpoena. They discovered references to the account buried in the more than 2 million pages of documents surrendered by Exxon.

A spokeswoman for Schneiderman declined to comment, saying the documents speak for themselves.

For the complete story, go to Inside Climate News.

David Hasemyer is a reporter for Inside Climate News.