Max M. Houck, Director at the District of Columbia Department of Forensic Sciences, has repeatedly defended the lab, even after prosecutors said they found flaws with the analysis. (Ricky Carioti/Washington Post)

One of the national organizations that govern DNA laboratories has ordered the District’s new crime lab to immediately suspend all DNA casework after concluding that the lab’s procedures are “insufficient and inadequate.”

D.C. Mayor Muriel E. Bowser ordered the audit by the ANSI-ASQ National Accreditation Board last month after the U.S. attorney’s office said it had discovered numerous errors in some of the lab’s DNA analyses. The audit, which was published Friday, criticized the lab’s practices and said they were not in compliance with FBI standards. It ordered “at a minimum” the revalidation of test procedures, new interpretation guidelines for DNA mixture cases, additional training and competency testing of staff.

The DNA analysts at the District’s Department of Forensic Sciences, according to the audit, “were not competent and were using inadequate procedures.” The authors of the review said the lab must begin to address the concerns within 30 days.

Legal experts say the audit could trigger a further investigation of hundreds of District criminal cases — including murder, sexual assault and gun possession cases — that have involved evidence tested at the lab since it opened in 2012.

In March, The Washington Post reported about alleged problems that prosecutors said they found in some of the lab’s DNA analyses. As a result, the city ordered an investigation of the lab’s practices.

The city-ordered audit was delivered the same week as the separate audit ordered by the U.S. attorney’s office. Forensic experts, commissioned by the attorney’s office, found similar problems.

Auditors from the accrediting group said they first discovered problems with the lab in 2013, a year after the lab opened in a $220 million facility in Southwest Washington. Lab officials then adopted corrective methods to address the concerns. But a year later, in 2014, problems arose again within the lab.

“It is apparent the corrective action plans that were put in place in 2013 were not effective since they occurred in 2014,” the analysts wrote.

The lab’s director, Max Houck, has repeatedly defended the lab, even after prosecutors said they found flaws with the analysis. Houck argued that his lab technicians followed the same protocols that many city and state labs across the country used in interpreting evidence.

Earlier this year, prosecutors stopped sending all DNA evidence to the city-run lab after finding what they called DNA-­analysis errors on several cases. The office began using outside labs and reviewing old cases. Bill Miller, a spokesman for the U.S. attorney’s office, said the office has ordered outside reviews of 182 cases, costing “hundreds of thousands of dollars” in federal taxpayer money.

After the audits were published last week, Houck said his office is “working diligently” to respond to both audits and that officials there take the reviews “seriously.” Keith St. Clair, a spokesman for the lab, said the processes that were identified as flawed “will be corrected.”

In an interview, Bowser (D) said that she was “very troubled” by the findings and that her office is working on its own “corrective plan” to address the concerns.

“We have an obligation to look at everything with a fresh set of eyes. That’s what we’re going to start” on Monday, she said.

Kenyan R. McDuffie (D-Ward 5), who is chairman of the D.C. Council’s judiciary committee, said “any deficiencies in the work performed by [the DNA lab] must be immediately addressed due to the broader implications of inaccurate forensic testing on the fair administration of justice in our courts.”

DNA analyses makes up 21 percent of the lab’s operations, the third-largest percentage of work for the lab, behind firearm and fingerprint analysis, St. Clair said. By ordering the suspension of all DNA analyses, D.C. police, Park Police, Capitol Police and the District’s office of the attorney general will have to find other labs to perform DNA work.

District officials spent Monday trying to identify an alternative lab to handle DNA examinations and assess such costs.

The D.C. lab was audited last fall by the same accreditation organization that the city used to perform the new review. Houck said his lab passed the previous audit by the group. The FBI also audited the lab last year, he said.

In an interview, Terry Mills, an accreditation manager for the board that issued the report, said the audits were only a “snapshot in time” of a lab’s operations and that board officials would have to be “camped out for about six months” to thoroughly investigate a lab’s procedures.

Mills said other labs across the country, including one lab last year, have been ordered to suspend their DNA testing and revamp their programs or risk losing their accreditation.

The problems with the District lab have centered on the analysis of evidence that includes DNA from more than one person — and their conclusions regarding the likelihood that a certain person’s genetic material is included in the sample.

In their initial findings earlier this year, experts contracted by the U.S. attorney’s office said the problem came to light when an outside expert reviewed the DNA analysis conducted in a rape case. The biggest mistake involved the analysis of DNA found on a stolen car’s gearshift, prosecutors said. D.C. analysts looking at the evidence found that the car owner’s DNA could have been on the gearshift and said the chance that a randomly selected person had the same genetic traits was 1 in 3,290. The outside experts said the more accurate finding was 1 in 9.

Acting U.S. Attorney Vincent H. Cohen Jr., who oversaw his office’s initial investigation into the lab, said DNA analysis is critical in securing not only convictions, but also exonerations.

“When done properly, DNA analysis is a powerful tool for holding criminals accountable and exonerating the innocent,” Cohen said in a statement. “The U.S. Attorney’s Office relies on leading scientists to ensure that we present only top-quality forensic science in court. We want D.C. jurors to know that the forensic evidence we present to them is based on solid science. That is why the Office acted quickly and decisively after its experts identified basic errors in the work done” by the lab.

In their report, two forensic specialists who reviewed the lab for the U.S. attorney’s office wrote that although variations in DNA analysis interpretation exist nationwide, they found times when the lab’s conclusions were “questionable.” In those instances, they wrote, differences between the lab’s findings and those of outside experts were not differences that “could be attributed to acceptable variation of DNA interpretation within the relevant scientific community.”

Defense experts say that although they commend the city and the U.S. attorney’s office for ordering the reviews, their biggest concern is the lack of standardization of how DNA mixtures are interpreted and that there is no universal standard in such interpretations.

“Thus the more important question here is whether DNA mixtures can accurately be interpreted by any forensic laboratory,” said Julia Leighton, general counsel for the District’s Public Defender Service.