Michael William Lutts, 50, pleaded not guilty in federal court Wednesday to a charge of sexually exploiting a child, said Darrell Foxworth, an FBI spokesman in San Diego.
Lutts was in federal custody and Foxworth didn't know the name of his attorney who could be reached for comment.
Lutts is a pediatric nurse in San Diego County. He was given custody of a 2-month-old, prematurely born foster baby Aug. 4, according to the FBI's criminal complaint.
He began molesting the boy the same day and recorded images and video on a cellphone that was seized during a search at his San Diego home Tuesday, an FBI agent stated in the complaint. Time stamps on the images indicate that the boy was molested for at least 10 days, according to the document.
"In my 28 years of being an FBI agent, it's one of the more disturbing cases," Foxworth said. "You look at the age of the victim here. This is a helpless child."
The FBI began investigating Lutts after he was linked to an email account that authorities believe was used to send child porn images to a suspected distributor, Foxworth said.
FBI investigators found more child pornography on computers, hard drives, CDs and other media, according to the criminal complaint.
Investigators planned to examine that material to identify other possible victims, Foxworth said. Because Lutts' job gave him access to children, investigators also were asking anyone with information to come forward.
Authorities also intend to look at the process by which Lutts was given care of the foster baby, who is now in protective custody, Foxworth said.