Republican senators who have criticized Judge Ketanji Jackson for her approach to sentencing child sexual abuse defendants offenders have focused on a single case from 2013 in which they argue she was inappropriately lenient on a teenager who pleaded guilty.

Here’s what happened in that case, United States v. Hawkins:

A high-school student downloaded pornographic images, and was arrested.

In 2012 Wesley Hawkins, an 18-year-old who was then in high school, started downloading pornographic images from the internet and, according to his lawyer, felt “confusion and shock rather than arousal.”

A gay boy from a religious family that strongly disapproved of homosexuality, Mr. Hawkins was driven by a kind of curiosity about the images and his connection to the people in them seemed, his lawyer said, to be “one of identifying” rather than of “exploiting them sexually.”

Many of images were, however, extremely disturbing, showing young boys engaged in a variety of sex acts, some of them violent. When Mr. Hawkins reposted some of the images onto YouTube, law enforcement officials got a “cyber-tip” about him and soon a police detective posing as a fellow child pornography collector reached out to him by email and suggested they trade images.

Prosecutors say that Mr. Hawkins eventually swapped images with the undercover detective, sending some files and asking for others that he believed were of the detective’s 12-year-old daughter.

Mr. Hawkins was arrested in June 2013, and prosecutors said he was immediately cooperative and “took full responsibility for his actions.”

Mr. Hawkins pleaded guilty and expressed remorse.

That September, Mr. Hawkins pleaded guilty to downloading and trading scores of images and movies containing child pornography, several showing boys who were under the age of 13.

After the plea, the case moved toward sentencing. In papers submitted to Judge Jackson, Mr. Hawkins’s lawyer, Jonathan Jeffress, argued that his client had indicated “no interest whatsoever” in the undercover detective’s repeated suggestions of a real-life sexual encounter.

Mr. Jeffress also submitted an evaluation by a psychologist asserting that Mr. Hawkins did not “demonstrate sexual deviation” but was instead driven to watch the pornographic images as “a way for him to explore his curiosity about homosexual activity and connect with his emotional peers.”

Prosecutors, in their own filing to Judge Jackson, said they considered the psychologist’s report and while they did not agree with everything in it, believed it provided “useful insights” about Mr. Hawkins’s “personal circumstances, family situation, and stage of development.”

Mr. Hawkins wrote Judge Jackson a brief letter saying how much he regretted what he had done.

“I have disappointed everyone in my family and everyone who has ever cared about me,” he wrote. “I hope that I can make up my mistakes and that this will not end my life before it starts. I swear that I will never do this again or any crime ever in my life.”

Prosecutors asked for a two-year sentence, calling the case ‘very unique.’

The sentencing was in November 2013.

The prosecution asked Judge Jackson to sentence Mr. Hawkins to two years in prison, arguing that his possession of the material was “extremely troubling and deserving of punishment.”

Mr. Hawkins’s lawyer asked for a single day in prison. He claimed that his client was young, remorseful and suffered from “emerging mental illness.”

Both sides told Judge Jackson that prior cases supported their arguments, and everyone agreed that the case was challenging and marked by what the prosecutor called “very unique circumstances.”

The prosecution mentioned cases in which at least two men who got child pornography from online chat rooms or from an undercover officer were sentenced to a full year in prison. The defense pointed to cases of men who had larger collections of illicit material than Mr. Hawkins did but did not serve prison time at all.

Judge Jackson handed down a three-month prison sentence, followed by six years of supervised release.

In the end, Judge Jackson — then in her first year on the federal bench in Washington — gave Mr. Hawkins three months in prison followed by more than six years of supervised release.

In making her decision — “a truly difficult situation,” as she put it at the time — Judge Jackson issued a sentence lower than the ones recommended by both the probation department and the nonbinding federal guidelines.

She also credited the defense’s claim that Mr. Hawkins should not be thought of as a pedophile because he was fairly close in age to the children depicted in the images he had.

While she acknowledged that Mr. Hawkins’s crimes were “serious” and “heinous,” she also said his case was not as troubling as others she had seen.

“I do not believe that you are similar in intent or as culpable as some of the depraved older adults,” she said.

The relatively lenient sentence was not unusual for child pornography cases — especially for those of defendants who possess such material, but are not involved in making it. Nor was the decision out of keeping with comparable cases in the Federal District Court in Washington where older defendants with larger child pornography collections have not served prison time at all.

Judge Jackson told Mr. Hawkins that the children in the pictures he possessed had been forced to commit “unspeakable acts” for “the gratification of sick people everywhere.” Some of them, she added, would never have a “normal adult relationship” while others might turn to drugs or vices “to deal emotionally with the pain.”

But Judge Jackson noted that Mr. Hawkins never produced any pornographic material himself and that he had only watched such material for less than a year. He was also young, remorseful and had the rest of his life ahead him.

“It is tragic that you permitted your curiosity to jeopardize all of that,” she said.