The trial of the former Oklahoma City police officer accused of a string of sexual assaults against black women began this week with an all-white jury.

Related: Investigation reveals about 1,000 police officers lost jobs over sexual misconduct

Daniel Holtzclaw is alleged to have sexually assaulted 12 women and a 17-year-old girl while on duty. Prosecutors have said he targeted middle-aged black women of limited means who had cause to want to avoid the police, such as outstanding warrants.

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Though African Americans make up 16% of the population of Oklahoma County there are no black people among the eight men and four women on the jury.

“We’re very disappointed that we don’t have any minorities on there … We’re not saying justice can’t prevail but we can be suspicious of it being [run] in a manner,” Oklahoma City National Association for the Advancement of Colored People (NAACP) president Garland Pruitt told KOCO local news, which reported that three black men were not picked from a pool of 24 potential jurors.

The racial composition of juries is attracting national scrutiny. On Monday the supreme court heard a case about alleged racial bias in jury selection during a 1987 murder trial that could impact the way jurors are picked in future; last month a judge in Kentucky dismissed an entire jury because he felt it was not representative of the community.

All-white juries in Oklahoma are “relatively uncommon but certainly not unheard of”, especially outside large urban areas, said Brady Henderson, legal director of the American Civil Liberties Union (ACLU) of Oklahoma.

In addition to exclusionary tactics such as peremptory challenges, Henderson said systemic factors risk making Oklahoma juries unrepresentative, especially in federal court where jurors’ names are taken from voter registration lists and a disproportionate number of black people are not registered. In state court, where Holtzclaw is being tried, names are culled from drivers’ licences and ID cards.

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Holtzclaw faces 36 charges, including rape, forcible oral sodomy and sexual battery, and could be sentenced to life imprisonment. He has pleaded not guilty.

Prosecutors contend that Holtzclaw began committing sex crimes in December 2013, when he coerced a hospitalised woman who was high on drugs and handcuffed to a bedrail into performing oral sex, with the promise that the charges would be dropped.

His youngest accuser said she was 17 when he raped her on her mother’s porch after groping her, ostensibly to search for drugs.

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A college football standout who became an officer after failing to reach the NFL, Holtzclaw worked a 4pm to 2am shift in northeast Oklahoma City. Detectives used GPS records from his patrol car to place him at the scene of the alleged crimes.

On Wednesday, the Oklahoman reported , a witness testified that Holtzclaw sexually assaulted her during a late-night traffic stop in June last year in which she feared for her life. She said that he unzipped his pants, took out his penis and told her: “I just got off work. I’m tired. I don’t have all night.”

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Her complaint to police sparked an investigation and the officer was arrested in August 2014. He was fired in January.

On Tuesday, his attorney, Scott Adams, said that the 28-year-old’s accusers “have street smarts like you can’t even imagine” and are not credible because of histories of criminal behaviour and drug addiction.

An Associated Press investigation unearthed about 1,000 officers nationwide who lost their law enforcement licences between 2009 and 2014 for sex-related incidents, including 550 for sexual assault.

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Last month a former Tulsa County sheriff’s deputy was found guilty of sexual battery and indecent exposure committed while on duty.

Henderson of the ACLU said calls for law enforcement in Oklahoma to wear body cameras had grown stronger since Holtzclaw’s arrest and that “everybody seems to be headed in that direction”.

Another effect of the case, he said, was a “degredation of trust between the police and the community”. A year ago, he said, callers to the ACLU asking about traffic stops would typically want to know their rights when being searched. Now a common question is “how do I protect myself from being raped or killed?”

The trial continues next week and is expected to last about a month.

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The Associated Press contributed to this report

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