D.C. Council Member Kenyan McDuffie on Wednesday renewed his criticism of the city’s inspector general for conducting an “anemic” investigation of test-cheating allegations in D.C. Public Schools.

In a strongly worded letter to Inspector General Charles Willoughby, McDuffie (D-Ward 5) requested permission to review confidential files compiled during that investigation. The probe lasted 17 months, focused on one school and found no evidence of widespread cheating.

“I am gravely concerned that your investigation did not reach further than Noyes Elementary School,” said McDuffie, a former prosecutor and chairman of the council committee that oversees the inspector general’s office.

McDuffie’s request came days after the publication of a 2009 memo that warned school administrators that teachers in as many as 70 schools might have cheated on standardized tests in 2008.

Chancellor Kaya Henderson and her predecessor Michelle Rhee both said they didn’t recall receiving the memo, which an outside consultant prepared. School system officials said the memo was based on incomplete information and the memo itself — based on an analysis of wrong-to-right erasures on answer sheets — cautions that more information would be needed to draw firm conclusions.

But McDuffie said the document raises questions about whether D.C. officials have adequately investigated long-standing suspicions of cheating.

“While I do not wish to make inflammatory accusations, the discovery of this memorandum creates doubt that your investigation thoroughly and expansively examined the allegations,” McDuffie wrote.

McDuffie first raised questions about Willoughby’s cheating investigation in January. The council member made clear in his letter Wednesday that he was unmoved by the inspector general’s explanation for limiting the probe to one school.

Two other investigations — by a DCPS-hired company and a federal inspector general — also found no evidence of widespread cheating, but neither examined the tests from 2008. Teachers and principals at schools that made large test-score gains that year were awarded thousands of dollars in bonuses.

McDuffie said there is an “alarming disparity” between the cheating probe in the District and a cheating probe in Atlanta, where officials interviewed 2,000 people before indicting 35 teachers and principals on cheating charges.

Willoughby could not be immediately reached for comment Wednesday evening. He will face council members Thursday morning when he testifies during a hearing on test integrity in the D.C. schools.

Also scheduled to testify are Chancellor Kaya Henderson; Jose Alvarez, chief of staff for the Office of the State Superintendent of Education; Abigail Smith, the Acting Deputy Mayor for Education; and John “Skip” McCoy, chairman of the D.C. Public Charter School Board.