BUFFALO, N.Y. -- A Lancaster man has been sentenced to more than 15 years in prison and a lifetime of supervised release on child pornography charges, according to the Western New York U.S. Attorney's Office.

Joseph Lombardo, 25, of Lancaster was arrested last year after an investigation found he had victimized three teenaged girls over a three year period, after meeting them on various internet websites.

One of the victims reported Lombardo reached out to her on the social media site Kik when she was 12 or 13 years old using the name of "Chris Richardson." He asked that the victim send him naked pictures of herself and threatened to post the pictures on the internet to exploit her if she didn't.

During a forensic analysis of a laptop found in Lombardo's Lancaster home, officers found images of another 13-year-old victim sent to Lombardo by a phone. She said Lombardo also identified himself as "Chris Richardson" when she met him on the website meetme.com.

"In a good cop, bad cop kind of way, another person would then come in, a different alias, who ended up being him, to try to foster some good will with these girls and get them to believe that this good cop would be able to get the bad guy to stop harassing them," said Assistant U.S. Attorney Aaron Mango.

Photos of a third victim, a 16-year-old, were found through a forensic analysis and it was discovered she sent 30 to 40 naked pictures of herself to Lombardo.

The FBI and Lancaster and Cheektowaga Police Departments assisted in the investigation.

Prosecutors say there were more photos of unidentified victims on Lombardo's devices. Anyone who may be involved is encouraged to come forward.