WASHINGTON (AP) — Mysteries remain about computer crashes inside the Internal Revenue Service and the government's efforts to recover all the missing data since the IRS acknowledged that it can't produce emails from seven officials connected to the tea party investigation.

The IRS commissioner is expected to face questions Friday from lawmakers for the first time about the missing emails.

The congressional investigation has been highly politicized because of allegations that the IRS inappropriately singled out tea party groups seeking tax-exempt status.

The IRS blames at least two separate computer crashes for the missing emails, which include those of a former IRS official at the center of the investigation.