WASHINGTON (AP)- The Interior Department's inspector general didn't find political interference by Vice President Dick Cheney on a key environmental policy in part because investigators weren't looking for it, an Interior official said Tuesday.

A 2004 report by the inspector general found no basis for a claim by then-Democratic presidential candidate John Kerry that White House political advisers interfered in developing water policy in the Klamath River Basin in California and Oregon.

But investigators did not ask about Cheney - and no Interior employee volunteered information about him, said Mary Kendall, deputy Interior inspector general. A former high-ranking Interior official, Sue Ellen Wooldridge, told The Washington Post that Cheney contacted her on a regular basis in 2001 and 2002, when the Bush administration was reworking water policy for the drought-plagued basin.

Wooldridge, who oversaw Klamath policy, never told investigators about her contacts with Cheney, Kendall said. And because investigators were focusing on White House political adviser Karl Rove - who was singled out in the Democratic complaint - they did not ask about Cheney, Kendall said.

“In the end, we don't know what we don't know,” she told members of the House Natural Resources Committee at a hearing exploring Cheney's role in the Klamath.

Democrats contend that Cheney - by intervening on the side of farmers who needed water for irrigation - contributed to a 2002 die-off of about 70,000 salmon, the largest adult salmon kill in the history of the West.

Republicans counter that there is no evidence that Cheney did anything improper, nor that his actions were to blame for the fish kill.

Cheney declined to appear at Tuesday's hearing and a spokeswoman had no comment.

Rep. Greg Walden, R-Ore., told Kendall he was “perplexed by the notion that maybe Dick Cheney did something in the background that you didn't spot.”

Wooldridge, who has since left government, could not be reached Tuesday.