A SEPTA transit police officer who prosecutors say viewed and shared child pornography for years — sometimes while on the job — has been charged with child sexual exploitation.

Brian Zenszer, 43, of Warminster, was arrested earlier this month after federal investigators learned he used the Kik messaging app to request and view dozens of child pornography files, including images of sexually abused prepubescent children, according to the criminal complaint.

A federal judge ordered Zenszer to remain in custody pending trial, court records show.

Zenszer’s attorney, Maranna Meehan, did not immediately return a request for comment.

Zenszer, who was fired after the criminal charges were filed, was a SEPTA police officer for 17 years, assigned to foot patrols throughout the transit system, primarily along the Broad Street and Market-Frankford lines, said SEPTA spokesman Andrew Busch.

“The allegations are disturbing and we are treating this matter with the utmost seriousness and urgency,” SEPTA said in a statement. “The individual was immediately placed on leave when the SEPTA Transit Police Department received notification from the FBI, and his employment was terminated.”

Omari Bervine, president of the Fraternal Order of Transit Police Lodge 109, the union that represents about 200 patrol officers, said the union does not represent Zenszer and declined to comment further.

The investigation was triggered by tips to Kik that two accounts associated with Zenszer shared child pornography, the complaint said.

After executing a search warrant for the accounts, federal investigators found 24 files containing child pornography in an account that Zenszer used to view and share images and communicate with others online, sometimes requesting videos of minors sexually abused, the complaint states.

When that account was closed by Kik, Zenszer opened another, and investigators found 16 additional child pornography images, according to the complaint.

Using the app, authorities said, Zenszer talked to others about child sex abuse videos. He also said he stole his girlfriend’s 12-year-old daughter’s underwear and masturbated in the child’s bedroom, according to the complaint.