On Thursday, the Supreme Court will consider whether to hear Mr. Dassey’s appeal.

The court has long said that “the greatest care must be taken” in making sure that confessions obtained from juveniles are voluntary. Mr. Dassey’s case could allow the justices to assess whether that command was taken seriously by courts in Wisconsin, which refused to suppress his confession.

It could also allow the justices to consider mounting evidence that false confessions from juveniles play a role in a disproportionate share of wrongful convictions. According to one study, 42 percent of exonerated juveniles had falsely confessed, compared to 8 percent of adults.

Mr. Dassey was interviewed for hours without a lawyer, a parent or any other adult who might have been alert to his interests. But the investigators who questioned him assured him that he had nothing to fear from them.

“Yeah, we’re cops, we’re investigators and stuff like that, but not right now,” said Tom Fassbender, a special agent with the Wisconsin Department of Justice. “I’m a father that has a kid your age, too. I want to be here for you. There’s nothing I’d like more than to come over and give you a hug.”

The investigators teased out contradictory statements from Mr. Dassey, steering him toward their theory of the case.