A man who once worked at the observation deck of the former John Hancock Center pleaded not guilty Monday to federal child pornography charges.

Christopher Colon is charged with receiving and accessing child pornography, federal court records show. He appeared in Chicago before U.S. Magistrate Judge Young Kim after being held in custody in Oregon.

Law enforcement targeted Colon in an undercover sting last year in which he offered free rides on the former Hancock building’s Tilt attraction, records show.

Posing as the father of two boys, 10 and 12, an undercover law enforcement agent responded to a Craigslist ad allegedly posted by Colon titled “Into perv/taboo chat, yng, fam (Chicago).”

In online messages that followed, Colon allegedly asked the agent, “Wanna meet just you and me, chat a bit and get to know each other? If we get along we can take it from there.”

Colon also allegedly told the agent he worked at the “observatory” and offered the purported father and his sons free turns on the “Tilt ride.”

In another exchange with an undercover FBI agent posing as a father with a 10-year-old son, Colon allegedly offered a free tour, drinks and snacks and a ride on the Tilt. He also allegedly said a private bathroom and office would be available “if you would like some special private time.”

A spokeswoman for the building said in a statement that, “multiple background checks were run on the employee in question, and no negative information was returned.”

Colon was convicted in January 2015 of aggravated child pornography in state court, the federal records show.