DENVER — A Denver-area medical doctor arrested by federal authorities earlier this month admitted that he secretly taped naked young boys while he examined them, Contact7 Investigates confirmed Wednesday.

Justin Bowen Neisler, 31, was arrested March 13 and charged with posting child pornography online after allegations he repeatedly posted images of underage boys involved in sex acts on social media.

Federal investigators are currently working to identify victims who may have been videotaped, said Jeff Dorschner, a spokesman for U.S. Attorney for Colorado Jason Dunn. Dorschner said it is too early to know how many victims there might be.

Court documents filed after Neisler’s detention hearing Tuesday say the doctor admitted to taping young boys.

“The defendant, a doctor, admitted to surreptitiously videotaping naked males as young as eleven years old during physical examinations,” court records read. “According to the agent, a review of these videos reflected that the defendant appeared to gain sexual gratification from the examinations.”

Court documents show that when federal investigators searched a location tied to Neisler, they found a "spy pen camera instruction manual" and a “black pen.”

The black pen is suspected by investigators to have been used to tape the young boys, a source with knowledge of the investigation told Contact7 Investigates.

Search warrant documents list the instruction manual and pen among other photography equipment taken from the location by investigators on March 13.

Neisler is licensed to practice medicine in Colorado and records list his place of practice as St. Anthony Family Medicine, located on the North Health Campus in Westminster.

Wendy Forbes, a spokesperson for Centura Health, which operates St. Anthony's, said in a statement that Neisler was fired after his arrest. The medical center is working with law enforcement in its investigation, Forbes said, and a third-party is reviewing the processes of its graduate medical education programs.

Authorities began investigating when the FBI received a tip from the National Center for Missing and Exploited Children that someone with an internet address matching Neisler’s home address uploaded child porn to the social media site Tumblr in October. He would allegedly re-post the pornography even after his original accounts were shut down, according to court documents.

According to documents, the charge against Neisler carries a mandatory minimum of five years in prison if he is convicted. The documents also state that "the government indicated it may be filling additional charges."

After the detention hearing Tuesday, the judge ordered Neisler be committed into custody and allowed to consult with his defense attorney. Denver7 left a voicemail Tuesday afternoon seeking comment from Neisler's attorney, Denver-based Martin Stuart, but has not received a response as of this story's publication.

"The Court further concludes by clear and convincing evidence that no condition or combination of conditions of release will reasonably assure the safety of the community," Judge Scott T. Varholak wrote.

The U.S. Attorney’s Office and the FBI are asking for the public’s help in their investigation. Anyone with information on this case can call 303-629-7171 ext. 1 or email denvermd@fbi.gov.