TULSA, Okla. (AP) — An internal investigation determined that a former police detective "grossly mishandled evidence" in the case of two Oklahoma brothers accused of fatally stabbing five of their relatives, according to Tulsa County's chief public defender.

Corbin Brewster discussed the internal affairs report during a Monday court hearing, saying it suggests former Broken Arrow Police Detective Gayla Adcock was overseeing the case when a computer hard drive with potentially significant evidence was lost. The report also indicates she violated legal requirements regarding the disclosure of evidence to his office, he said.

Adcock resigned last month during the investigation of her actions surrounding the lost evidence, the Tulsa World reported.

Brewster's office sought to have Adcock subpoenaed to testify about the work she did on the investigation related to Michael Bever, 19, and his brother, 21-year-old Robert Bever, who police said fatally stabbed their parents and three of their younger siblings in 2015. Michael Bever is scheduled for trial next month.

Brewster told District Judge Sharon Holmes during Monday's hearing that it appeared Adcock had "left town."

Adcock signed a document indicating receipt of evidence when she went with two other officers to retrieve evidence from the Oklahoma State Bureau of Investigation in Oklahoma City. But she didn't log each item transported to Broken Arrow, according to her attorney, Scott Wood.

Brewster said Adcock acquired the evidence in December 2015, but he wasn't made aware any of it was missing until October 2017.

Holmes said the case against Michael Bever doesn't solely revolve around Adcock's actions, which she called "frustrating and disturbing." The judge told both sides she wants to resolve other pretrial matters before returning to the issue of the missing evidence.

Michael Bever, who was 16 at the time of his family members' deaths, has pleaded not guilty to five counts for first-degree murder. He was charged as an adult. His trial is scheduled to begin in April.

His brother pleaded guilty in 2016 and was sentenced to life in prison for the attack, which also wounded their younger sister. Another sister was unharmed.

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Information from: Tulsa World, http://www.tulsaworld.com