A Westbury man was arrested Thursday after downloading child pornography in May, Nassau police said.

Sergio D. Barreno, 49, of Dayton Street, pleaded not guilty Thursday when he was arraigned on one felony count of possession of a sexual performance of a child, defined as someone under 16.

Detectives focused on Barreno after getting a report from the National Center for Missing and Exploited Children that child pornography images had been downloaded to a Westbury address, police said.

Barreno’s attorney, John Powers Jr. of West Islip, said he was unaware of any search warrant in the case and questioned how police could have known his client had downloaded anything without examining his electronic devices, including hs cellphone.

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Powers said he did not have details of the case because he was unable to speak at length with Barreno and because authorities gave him only a “scant amount of information.”

When police knocked on Barreno’s door Thursday morning, his client had no idea why they would arrest him, the attorney said.

“Mr. Barreno is innocent until proven otherwise,” Powers said. “I ask the public to keep an open mind. It’s very early in the case and we don’t know much about it. There’s always more than one side to the story.”