UPDATE: U.S. District Judge Virginia Hernandez Covington has sentenced William Napolitano to life in prison.

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The school bus manager and the assistant principal were trusted Pasco County education professionals who authorities say shared an interest in sexually abusing children.

Prosecutors say William Napolitano and Kyle Ritsema knew each other long before their separate arrests on federal child pornography charges. Both resigned from the school district after their arrests.

A memorandum filed in advance of Napolitano's sentencing, set to take place Thursday in the Sam M. Gibbons Federal Courthouse in Tampa, alleges the pair did more than exchange illicit images of kids. They preyed on them, too.

"The two constantly traded war stories about sexually abusing children and conspired to have group sex with minors," the document states.

Ritsema, 35, was an assistant principal at Cypress Creek Middle/High School in Wesley Chapel before his February arrest. A criminal complaint alleges he admitted to making pornographic images of a teenage boy. A change of plea hearing in his case is scheduled for Dec. 21.

Napolitano, also 35, was arrested in 2017 and signed a plea agreement in August in a separate case, admitting to conduct that Assistant U.S. Attorney Francis D. Murray described in a sentencing memo as "an ongoing campaign to have sex with minors," and a long-term predatory sexual relationship with a boy who was 15 when they met.

He took pornographic pictures of the boy without his knowledge and shared them with others, the memo states. The images became part of Napolitano's vast child pornography collection, which the memo said featured victims as young as infants being subjected to sadistic sexual abuse.

Prosecutors are seeking a life sentence for Napolitano. They believe he victimized other children.

"Napolitano's mind has descended to depths of depravity that are hard to fathom," Murray wrote. "He poses a constant and perpetual threat to society. His freedom and autonomy are fundamentally incompatible with the safety of children in our community and elsewhere."

Napolitano was a transportation manager with Pasco County schools when he was arrested in October 2017. He had worked for the district more than a decade, starting as a school bus driver in 2004. Before that, he was a child care worker for the YMCA in New Port Richey, according to the memo.

Federal agents became aware of him during a separate investigation into child pornography that was being traded through Kik, an instant messaging application. An undercover agent had several sexually explicit conversations with a person who used the screen name "routemeup." The name was registered to a "William Snyder," but an investigation linked the internet protocol address to Napolitano.

Investigators later raided his New Port Richey home. On his iPhone, a laptop and a DropBox account, they found hundreds of pornographic images. Prosecutors described the collection as "staggering," both for its size and the depravity of its content.

"Napolitano admitted having a deep interest in this type of material," the memo states. "Particularly pornography involving infants and toddlers."

Text messages stored on Napolitano's phone included conversations with other people, wherein he boasted about his exploits with teenage boys, according to the memo. One of those he chatted with was Ritsema.

"Napolitano and Ritsema were well aware of each other's positions and corollary obligations to protect and nurture children in the community," the memo states.

It quotes one exchange from June 2014, in which the pair planned to watch child pornography together.

"Please don't tell anyone," Ritsema wrote, according to the memo. "It'd be all over the news. I won't say anything either!"

"Our secret dude," Napolitano replied.

Ritsema was aware that Napolitano was involved in an inappropriate relationship with a teenage boy, the memo states, and they discussed Ritsema taking part.

The boy was 15 and a student in a local school when he met Napolitano on a social networking application, according to records. Starting in 2014, Napolitano engaged in an "ongoing enticement" of the boy, having sexual conversations with him and soliciting nude photos. On several occasions, he sexually abused the boy in his car while parked in public places, the memo states. Another time, Napolitano sneaked into the teen's bedroom, which he shared with two younger brothers, and sexually abused him there.

The memo noted that Napolitano also had "a bizarre fascination with intentionally acquiring and spreading HIV."

In a conversation with law enforcement, the victim recalled one occasion after he turned 18 in which Napolitano took him to a hotel to meet two other men for intercourse. The boy said he didn't participate because one of the men appeared to be ill.

Prosecutors detailed "strong circumstantial evidence" that Napolitano molested other children. In his text messages, he made references to having sexually abused at least five other young victims, according to the memo. They include a 13- or 14-year-old boy from Tarpon Springs, a 16-year-old boy from East Lake, and another teen Napolitano claimed to have sexually abused at a Wesley Chapel golf course.

Federal agents have tried to identify those other victims. They scoured school yearbooks, questioned teachers, and interviewed his cellphone contacts but were unsuccessful.

"Napolitano was responsible for protecting the safety of children in the community as they commuted to and from school each day," the memo states. "He instead preyed on them. His conduct has shaken public confidence in both the safety of children in our public school systems and the laws designed to protect children at large."

Contact Dan Sullivan at dsullivan@tampabay.com or (813) 226-3386. Follow @TimesDan.