Sgt. Kreg Costa was arrested Thursday in Broward County, Florida.
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Officials became suspicious when Costa was allegedly found in his office with the lights off several times, his uniform and gun belt removed.
In spite of a reprimand, Costa allegedly continued to inappropriate behavior.
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A hidden surveillance camera allegedly caught Costa viewing hardcore pornography during his shift, including websites featuring underage girl and incest-related material.
Investigators say Costa used social media to prey on young girls, and reached out to a 15-year-old victim in California.
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Costa is accused of exchanging lewd photos with the girl, some of which were found on his work laptop.
In all, investigators say more than 150 photos and several videos of minors were discovered in the sergeant's possession.