The first defendant in the Atlanta Public Schools test cheating scandal was found not guilty Friday, dealing a blow to prosecutors’ efforts to hold those allegedly involved criminally responsible.

A jury acquitted Tamara Cotman, a former area director with oversight of 21 schools in north Atlanta, of charges that she influenced a witness who claimed Cotman instructed principals to tell investigators to “go to hell.”

“I feel vindicated,” Cotman said after walking out of the courthouse. “I’m very much grateful to those who have been very supportive. … I’ve always said that I serve a God of truth and that the truth will set you free. And today I feel free.”

A juror, Ben Emerson, a 28-year-old research engineer from Atlanta, said prosecutors presented a strong case about test cheating, which Cotman was not standing trial for.

“I wouldn’t say there was too much evidence, but there was a lack of evidence for the charge that was brought on this person,” he said.

Fulton District Attorney Paul Howard complimented his trial team, saying its presentation in the courtroom was outstanding.

“We are disappointed with the verdict,” he said. “This is just one part of what we always thought would be a very long battle and what we understand is a very complicated case.”

Cotman’s successful defense may have weakened the case against those facing charges on allegations of falsifying standardized test scores. Earlier this year, prosecutors obtained a sweeping racketeering indictment against nearly three dozen former APS executives and teachers, including former Superintendent Beverly Hall.

Cotman’s acquittal after a three-week trial may embolden other defendants to continue fighting the charges rather than seek plea deals. Their trial is scheduled for next spring.

Cotman’s attorney, Benjamin Davis, argued during the trial that her case wasn’t about cheating even though prosecutors made it seem that way. He said Cotman never witnessed cheating or any other criminal behavior, and she didn’t attempt to stonewall investigators.

Prosecutors had claimed that Hall and school system lieutenants such as Cotman wouldn’t accept failure on high-stakes tests mandated by the federal government, and they resorted to cheating both to save their jobs and to collect incentive pay for meeting targets.

Cotman stood trial on a single felony count: influencing a witness.

She was accused of intimidating and threatening Scott Elementary School interim Principal Jimmye Hawkins, who feared retaliation if she cooperated with the state investigation into test cheating. If found guilty, Cotman would have faced up to five years in prison.

Hawkins testified that Cotman opened a Nov. 17, 2010, principals meeting with a lengthy rant against the GBI’s investigation. Cotman then handed out memos labeled “go to hell” to the 10 principals, directing them to address them to the GBI or state investigators, Hawkins testified.

But other principals in the meeting told jurors during the trial that the memos were intended as a stress relief exercise, and Cotman didn’t mention the GBI.

Her trial was a test case of what’s to come against other educators facing charges.

The prosecution walked jurors through the history of cheating in Atlanta Public Schools, calling witnesses including children who couldn’t read at grade level and teachers who admitted changing answers.

The state investigation Cotman was accused of interfering with concluded in July 2011 that 185 educators had participated in cheating or should have known about it.

Fani Willis, the chief assistant district attorney, said jurors needed to understand “there was cheating going on” to prove that Cotman wanted to cover it up.

The victims, Willis said, were children who didn’t get academic help because they scored well on tests.