Washington, Sep 30 (IANS): US lawmakers requested documents from Volkswagen and the US Environmental Protection Agency (EPA) regarding the aurtomaker's illegal software used to mask emissions for certain models of its diesel cars.

In a letter to Michael Horn, CEO of Volkswagen Group of America, the bipartisan leadership of the House Energy and Commerce Committee on Tuesday asked VW to turn over all documents, including those "related to the development, approval, testing and use of the software" installed in its nearly 500,000 diesel cars in the US, Xinhua news agency reported.

In a separate letter to the head of the EPA, the committee leaders asked for a detailed timeline of events and activity related to the violations, including how and when the violations were discovered.

"It seems Volkswagen had a dirty little secret, and it is not just consumers who are feeling betrayed," said a joint statement by the committee's chairman Fred Upton and the committee's oversight and investigations panel chairman Tim Murphy.

"There are many unanswered questions and we will get the facts and the answers that the American people deserve."

The committee wants the information and documents by October 13. The requests came on the heels of last week's announcement that the committee will soon hold a hearing on the Volkswagen scandal.

The software in question, which the company acknowledged deploying in some 11 million vehicles worldwide, allowed Volkswagen's diesel cars to detect when they were undergoing emissions testing and turn full emissions controls on only during the test.

This resulted in vehicles meet emissions standards in the laboratory or testing station, but during normal operation, emit nitrogen oxides at up to 40 times the standard.