Updated

A senior Pentagon official is criticizing the House Republican-led investigation into the deadly September 2012 attacks in Benghazi, Libya, over a "crescendo" of requests to the Defense Department.

In an April 28 letter, Stephen C. Hedger, an assistant secretary of defense, expressed frustration with the panel's potentially futile requests for witnesses and information. He also challenged a line of questioning that focused on hypotheticals. Hedger suggested that the final committee report may be based on speculation rather than fact.

Hedger complained that the committee asked the Pentagon to track down four pilots who didn't deploy to Benghazi. The panel also sought an interview with a mechanic who claimed on his Facebook page that planes could have been sent to Benghazi in time.

Four Americans died in the attacks.