If police think someone has child pornography on his computer, should investigators be able to force him to provide his passwords - or would that violate his constitutional right against self-incrimination?

That issue was at the heart of an appellate hearing Wednesday in federal court in Philadelphia in the case of Francis Rawls, a former Philadelphia police sergeant, who has not been charged with a crime but who has been in custody for nearly a year in contempt of court for failing to unlock his encrypted electronic devices.

The case has attracted national attention from prosecutors, defense attorneys, and legal advocates for its potential ramifications on fundamental concepts including privacy, self-incrimination, and unreasonable search and seizure.

And as three appellate judges on Wednesday probed the positions of government lawyers and Rawls' defense team, some of their questions suggested that they, too, were grappling with the complicated matters at the center of the case.

"Are you asking us to ignore the Fourth Amendment?" asked Judge Thomas I. Vanaskie of the U.S. Court of Appeals for the Third Circuit.

It was one of two amendments the judges regularly referenced during the hearing. The other was the Fifth Amendment, which Rawls' attorneys believe protects his right to keep his passwords to himself.

The case began in March 2015, when detectives with the Delaware County District Attorney's Office identified him as a suspect in an investigation of a website called Freenet, according to court documents.

The site allegedly allowed users to share child pornography, and investigators said data showed that devices owned by Rawls - referred to as "John Doe" in the documents - had been routing or requesting such files.

But after authorities seized electronic devices from Rawls' home - including an iPhone, an Apple Mac Pro computer, and two external hard drives - they were unable to unlock the hard drives, which also were encrypted, documents say. The labeling of some files caused investigators to believe that the hard drives contained thousands of examples of child pornography, the documents say.

Rawls later was ordered to give authorities the passwords to the hard drives, but said he couldn't remember them.

On Sept. 30, 2015, a federal judge - who did not believe Rawls' explanation - found him in contempt of court and ordered him taken into custody, according to court documents. The next month, Rawls was fired from the Police Department.

Nathan Judish, an assistant U.S. attorney, argued Wednesday that a computer password was like a key to a safe, which authorities can force suspects to turn over if police already know what's inside.

But Rawls' attorney, Keith M. Donoghue, argued that investigators have not sufficiently proven that Rawls has specific material on his hard drives. Even if they had, Donoghue said, a password is not the same a physical key, because providing the password to police would be like being forced to provide self-incriminating testimony.

"It's a memorized security code that exists in his own mind, and therefore is protected by the Fifth Amendment," Donoghue said.

The judges - Vanaskie, Kent A. Jordan, and Richard L. Nygaard - challenged attorneys for both sides on their positions, as well as Mark T. Rumold, a lawyer for the Electronic Frontier Foundation, who supported Rawls' defense.

At times, the jurists questioned whether a mandated password disclosure could lead to other issues, such as finding evidence of different crimes on the unlocked device. That concern prompted Vanaskie's question about whether a Fourth Amendment violation against unreasonable searches and seizures could result from being forced to hand over a password.

Attorneys for both sides declined to comment after the hearing, and the judges did not offer a ruling or a time frame for when they would.

Rawls did not attend the hearing. He remained in custody at the Philadelphia Federal Detention Center, according to prison records.