convicted sex offender accused of keeping more than 100 images of child pornography at work was sentenced Wednesday to 15 years in prison and will be reclassified as a sexual predator.

Gainesville Police arrested Robert A. Costello, 58, in January after investigators reportedly checked computers where he worked and found he had visited Web sites showing child pornography. Officers also found he had disks with more than 2,000 pornographic images, about 100 images of children, according to Alachua County court records.

In December 2004, probation officers also searched Costello's home and reportedly found explicit writings about a father having sex with his teenage daughter.

Costello entered a no-contest plea to violating his probation, ordered after his 2003 conviction for lewd and lascivious assault of a 10-year-old girl, and to charges related to the officers' discovery of the pornographic images.

Circuit Judge Peter Sieg sentenced Costello to prison for violating his probation. His prison term will be followed by two five-year terms of sex-offender probation to be served consecutively for the recent charges, according to Assistant State Attorney Andrea Muirhead.

At the time of his arrest, Costello had been working as a part-time secretary at an area church.

A church official said after Costello's arrest that he was aware of the man's criminal history, but Costello had been hired because he was receiving treatment and regularly attending church.

A court designates someone a sexual predator who is convicted of either one first-degree felony sex crime or two second-degree felony sex crimes. The latter must occur within 10 years of the previous offense, conviction or release from court sanctions, according to the Florida Department of Law Enforcement.

Lise Fisher can be reached at (352) 374-5092 or fisherl@gvillesun.com.