WASHINGTON (AP) — After years of following the paper trail of $51 billion in U.S. taxpayer dollars provided to rebuild a broken Iraq, the U.S. government can say with certainty that too much was wasted. But it can't say how much. In what it called its final audit report, the Office of the Special Inspector General for Iraq Reconstruction Funds on Friday spelled out a range of accounting weaknesses that put "billions of American taxpayer dollars at risk of waste and misappropriation" in the largest reconstruction project of its kind in U.S. history. "The precise amount lost to fraud and waste can never be known," the report said. The auditors found huge problems accounting for the huge sums, but one small example of failure stood out: A contractor got away with charging $80 for a pipe fitting that its competitor was selling for $1.41. Why? The company's billing documents were reviewed sloppily by U.S. contracting officers or were not reviewed at all.