“On the contrary, we were convinced she did know,” the foreman told The Sentinel, asking to remain anonymous and saying he was speaking on his own behalf. “She may not have known what day, or what location, but she knew. However, we were not tasked with deciding if she was aware of a potential attack. The charges were aiding and abetting and obstruction of justice.”

And on those charges, he said, the jury was presented with “no option” but to acquit.

In federal court, where terrorism defendants often accept guilty pleas before going to trial, prosecutors rarely lose cases. A report last year by the Center for National Security at Fordham University School of Law found that, while Islamic State-related cases are more likely to go to trial than federal cases in general, every case that was resolved between March 2014 and August 2017 resulted in a conviction. The national average conviction rate is 92.5 percent, according to the report.

Image Omar Mateen killed 49 people and wounded 53 others in a June 2016 attack on an Orlando, Fla., nightclub. Credit... via Associated Press

But prosecutors generally have been cautious about filing charges against possible accomplices in terrorism cases. Though an accomplice is sometimes the only one left alive to prosecute, such cases can be difficult to prove.

“Prosecutors have got a duty not to be caught up in hysteria,” said William N. Nettles, who was the United States attorney in South Carolina when a white supremacist killed nine black churchgoers in Charleston in 2015 and successfully prosecuted a man who had withheld information about that attack.

He said prosecutors must guard against allowing public emotion to influence their decisions.

“The federal government should never lose a case,” Mr. Nettles said. “Prosecutors should never lose. They pick the fight, they pick the day the fight happens, they’ve got the best investigative capabilities in the world. It should always be an embarrassment for the government to lose.”

After the verdict, two of Ms. Salman’s defense lawyers, Charles D. Swift and Linda Moreno, said in an interview that prosecutors had offered their client a plea deal in the weeks leading up to the trial but she had refused to accept it, insisting on her innocence.