Mitchell continued, so Atherton told the bailiff, "Let's just take Mr. Mitchell away."
After officers escorted the still-singing street preacher from the courtroom, the judge observed with a laugh, "He sings well."
She said she was familiar with the hymn - often heard at Christmastime - and noted that Mitchell knew the correct words.
But the odd performance may also give insight into Mitchell's mental state, which, according to his defense team, has recently deteriorated.
Atherton reluctantly agreed to allow two court-appointed mental health experts to re-evaluate Mitchell. But Atherton insisted the process - which initially took seven months to complete - does not need to start again at "square one."
Noting that a Feb. 1 trial date is still on, Atherton said she wanted the new competency reports filed in time for a Jan. 6 hearing. As defense attorney Vernice Trease noted, the experts may be required to testify, if they fail to agree about Mitchell's condition.
Because those same two court-appointed experts had previously disagreed about Mitchell's competency, they were scheduled to testify three months ago. But when Atherton refused to hold the hearing in secret, Mitchell's defense team stipulated - or agreed - that he was competent.
The defense stipulation was also prompted by a report from their own independently hired expert, who found Mitchell competent. That expert, Jennifer Skeem, recently re-interviewed Mitchell in jail and claims his ability to make reasoned legal choices had declined.
Atherton claimed Skeem's findings were hearsay because they were relayed to the court through an affidavit penned by defense team member Heidi Buchi.
But Trease noted that Skeem was the only one of the three experts who had actually talked with Mitchell, who has refused to speak with the court-appointed evaluators.
Asked later about Mitchell's behavior, Deputy Salt Lake County District Attorney Kent Morgan told news reporters, "I'll leave that to the psychiatrists. [It could be] evidence of someone choosing to sing, or someone who's nuts."
Mitchell's behavior might also have been a form of protest for being forced to come to court. Friday's hearing was delayed 35 minutes because Mitchell refused to be transported. When Atherton heard of his refusal, she reportedly ordered him to be brought against his will.
The song choice also may be significant because Mitchell has called himself "Emmanuel" or "Immanuel," the name he used while doing odd jobs at the Smarts' Federal Heights home in November 2001.
The June 2002 knife-point kidnapping of Elizabeth and the attempted kidnapping of her 15-year-old cousin from her Salt Lake County home in July 2002 were allegedly prompted by Mitchell's effort to fulfill his own prophecy that he would take seven plural wives, according to police.
Mitchell, 50, and his wife and co-defendant, Wanda Eileen Barzee, 59, are each charged with kidnapping and sexual abuse.
Nine months after she disappeared, Elizabeth was found walking on a Sandy street with Mitchell and Barzee.
Found incompetent by two mental health evaluators, Barzee is being treated at the Utah State Hospital.
Meanwhile, it was revealed Friday that Mitchell's defense team has recently filed six motions under seal, meaning they are not publicly accessible. Four of the motions pertain to the legality of Mitchell's grand jury indictment, said prosecutor Clark Harms.
Atherton said it was not the prerogative of attorneys to decide what is filed under seal. "The presumption is that these proceedings are open," Atherton added.
The sealing of the motions, along with numerous other pre-trial issues, is scheduled to be discussed Jan. 6.