A former New York City school teacher is facing criminal charges in what appears to be the first prosecution stemming from an FBI investigation of nearly 215,000 users of a child pornography website that authorities seized earlier this year.

Alex Schreiber, 66, was arrested on a federal charge of knowingly possessing child pornography and later released on a $100,000 bond following an appearance in federal court in Brooklyn, New York.Schreiber, a resident of the New York City borough of Queens, visited the website under the user name “philsic,” logging in for 194 hours from September to March, a criminal complaint said.

In one instance, Schreiber accessed a post containing a link to about 400 images of an approximately 5-year-old girl engaged in various sexual acts, including with an adult man, the complaint said.

The case against Schreiber, who was previously a math teacher at William Cullen Bryant High School, appeared to be the first brought so far in a major online child pornography probe involving a secret website.”Website A,” as it was called in court documents, began operating around August 2014 and contained thousands of postings and messages featuring child pornography images and had 214,898 members, according to a court filing.

A search warrant application indicated that, as a result of that probe, authorities had sought in June to search the apartment of a Brooklyn man, who has not been charged.

Those websites, according to court documents, operated on the Tor network, which allows users to communicate anonymously.