Responding to the criticism, Gary Oldenburger, the county attorney for Wapello County, defended the sentence in a statement dated Thursday, presenting Mr. Grooms as the unwitting lackey of child pornographers who tricked him into the assault, as they had done to hundreds of other children.

By pretending to be a girl his age, then 16, the two men, one in New Orleans and one in Ireland, persuaded the teenager to perform sex acts he wouldn’t otherwise have done, Mr. Oldenburger said.

Mr. Grooms did not know he was being recorded, the prosecutor said in the statement.

He added that the child was uninjured, no pain was inflicted, and the child was too young to be aware of what was happening. Though the crime was no “less horrible because the child was too young to understand,” the lack of injury is an important factor in sentencing, he said.

Mr. Oldenburger said the case likely would have been dismissed had it gone to trial. The parents of the victim did not want Mr. Grooms to serve significant jail time and were more focused on him receiving treatment, he said.

The prosecutor also said that important witnesses were unwilling to testify, so the video might not have been admissible as evidence, making a trial more difficult.

He said a long sentence likely would have been overturned on appeal, with a quick parole. The 860 days he had already spent in jail would have counted toward his time served.

Mr. Oldenburger said psychologists did not believe Mr. Grooms was a high-risk candidate for committing more offenses.

“If Grooms was sent to prison for a long period of time rather than being sentenced to probation, he more than likely would be a greater risk to the community after his release than he will be after serving the sentence he received,” he said.