Evidence in 48 sexual assault cases was improperly destroyed by Aurora police officers who failed to follow protocols, and officials are continuing to investigate whether any additional cases have been affected by what Aurora Police Chief Dan Oates called “a grievous mistake.”

In one case, DNA evidence had identified a suspect and investigators were moving toward an arrest, Oates said.

Prior to a Tuesday news conference, Oates and prosecutors from the 18th Judicial District Attorney’s Office met with the woman and told her that the case could no longer be prosecuted.

Oates said the victim was “gracious and understanding. More understanding than I would have been in that situation.”

“Obviously this is not a good day for the department,” Oates said. “This is a big mistake.”

During the news conference, Oates said the evidence, all from 2009 cases, appeared to have been destroyed during a six-month window beginning last January.

No additional evidence has been destroyed since the errors were discovered two weeks ago.

Many of the cases in which evidence was destroyed did not have a current likelihood of prosecution, Oates said. Several victims had selected not to pursue their cases.

The police department collects an average of 50,000 pieces of evidence and property each year. Every year, in order to create space for new evidence, an equivalent amount of evidence must be disposed of.

Under a law passed in 2009, officers in the department’s Property and Evidence Unit adopted polices that tightened the requirements for the destruction of evidence.

In 18 of the sexual assault cases, the lead detective recommended the destruction of the evidence, but follow-up reviews, required under the law, never occurred.

Evidence in the other 30 cases was incorrectly destroyed by an officer assigned to light duty in the unit.

None of the errors was intentional, Oates said, adding that he suspects improper training may be an issue.

“We will do all that we should to fix this problem,” he said. “No one — including that officer — intended this outcome. It was a mistake.”

In addition to the case that cannot be prosecuted, DNA samples in a second case matched those collected in two separate sexual assaults in Denver. If a suspect is ever charged in those cases, it would be difficult “but not impossible” to prosecute the Aurora case, Oates said.

“Obviously, we have a problem we need to fix,” he said.

An expert panel will review the matter and make findings and recommendations to the Aurora Police Department. The panel will include representatives from the state Attorney General’s office, a DNA expert and prosecutors from the 17th and 18th district attorneys’ offices.

“We are participating in an independent task force that will individually review the cases potentially affected by these evidentiary issues,” George Brauchler, district attorney for the 18th Judicial District, said in a statement.

Sean McDermott, president of the Colorado Criminal Defense Bar, said he was encouraged by Oates’ pro-active approach to the errors, as well as the department’s selection of panel members for the independent review.

“When evidence is lost, it is not only about the conviction of the guilty but the freedom of the innocent,” McDermott said.

Oates said the department immediately focused on the sexual assault cases affected by the errors because of their high importance, and now the department will expand its review to see what additional cases may have had evidence destroyed.

Jordan Steffen: 303-954-1794, jsteffen@denverpost.com or twitter.com/jsteffendp

Denver Post staff writer Sadie Gurman contributed to this report.

The members of the review panel are:

Aurora Deputy Chief Terry Jones, chairman

Colorado Senior Assistant Attorney General Julie Selsberg

Retired Colorado Springs Police Chief Richard Myers, a former commissioner at the national Commission on Accreditation for Law Enforcement Agencies

Colorado State University Chief of Police Wendy Rich-Goldschmidt

Chief Deputy District Attorney Ann Tomsic, 18th Judicial District

Aurora Police Cmdr. Fran Gomez

Still to be named is a senior assistant to be assigned by 17th Judicial District Attorney Dave Young

