Scolded by the Court

The Times identified more than 30 instances of judges criticizing prosecutors or federal agents for conduct such as destroying or withholding evidence, violating rules about communications with jurors and making false or exaggerated claims, including some disproved by videos.

Judges have denounced the government’s actions as “flagrant,” in “bad faith” and “shocking to the universal sense of justice.”

One case of evidence being destroyed took place last September in San Bernardino, Calif. Federal agents were following a Nicaraguan man, Joseph Blandon-Saavedra, who was driving to work in a Toyota Corolla. At an intersection, the agents boxed him in with their two cars, smashed his window and arrested him.

All three vehicles were damaged. Mr. Blandon-Saavedra said the agents had hit his car when they cut him off. But the government said he had rammed them, and prosecutors charged him with two counts of assaulting officers with his sedan.

Mr. Blandon-Saavedra’s lawyers asked that the cars be preserved so their expert could examine them. But agents immediately repaired one of theirs.

The judge dismissed the count tied to the repaired vehicle, calling the agents’ actions part of a “growing pattern of mishandling evidence” that might undermine officers’ assault claims. Prosecutors appealed the dismissal. The count related to the other government vehicle is pending.

In April, a federal judge in Los Angeles threw out assault charges against two protesters, in the middle of a trial, after finding that prosecutors had failed to turn over internal “use-of-force” reports that could have been helpful to the defense. A month later, the government dropped charges against six protesters in Chicago after a judge criticized prosecutors for having mishandled a grand jury, partly by speaking to jurors outside the courtroom.

In Laredo, Ariana Guadalupe Garcia, a 19-year-old American, arrived at a border crossing last July to meet her young niece. Ms. Garcia, who had come from the U.S. side, had clothes for the girl to bring back to a relative in Mexico to sell, a common exchange at border crossings.

But Ms. Garcia found that the girl, who had arrived from Mexico, was being held in an inspection area, and when she tried to speak to her through a window, an officer told her to leave. Ms. Garcia did not immediately obey, prompting several other officers to approach her. After some back-and-forth, the officers began escorting Ms. Garcia away, according to court records.

As they passed through a short stretch of walkway with no working security cameras, Ms. Garcia took at least one photo with her phone. An officer swatted it away. Prosecutors said that Ms. Garcia then hit an officer on the arm and another in the ear, which she denied. She was arrested and later charged with assault.

Afterward, an officer told her to delete the photo she’d just taken, going so far as to watch her permanently erase it from the Recently Deleted folder.

The case against Ms. Garcia began to fall apart when the judge asked how prosecutors intended to prove she had hit anyone — especially since security footage from right before the alleged incident showed no sign of her acting violently toward the four male officers.

The deleted photos were the final straw.

“The government acted in bad faith in destroying the evidence,” the judge wrote, “further demonstrating that Ms. Garcia’s constitutional rights have been violated.”