From CNN:

In a letter to Rep. Darrell Issa, R-California, and Sen. Charles Grassley, R-Iowa, Assistant Attorney General Ronald Weich suggested that sensitive information relating to ongoing investigations is coming from their staffs.

Information from the documents appeared in news reports after it was shared with the lawmakers’ staffs, he said.

“While we do not know who provided these letters to reporters, we are deeply disturbed that the sensitive law-enforcement information contained in them has now entered the public realm,” Weich said. “This public disclosure is impeding the department’s efforts to hold individuals accountable for their illegal acts.”

As was predicted by some at the time an internal DoJ investigation was launched, it is being used to impede the Congressional investigation.