ST. JOHNS COUNTY, Fla. -

A 30-year-old St. Johns County man pleaded guilty Thursday to nine counts of producing child pornography, U.S. attorneys announced.

On each of these counts, Lucas Chansler faces a minimum mandatory sentence of 15 years, up to 30 years in federal prison, $250,000 in fines and a potential life term of supervised release, authorities said.

According to court documents, beginning in or about 2007 and continuing until on or about Jan. 8, 2010, Chansler used computers and interactive computer services to send threatening communications to several girls across the U.S.

Chansler transmitted the threatening communications with the intent to extort things of value from the girls, including digital photographs and webcam videos of the girls in various states of undress, exposing themselves and engaging in sexually explicit conduct, according to U.S. attorneys.

Authorities said Chansler engaged in a pattern of extortion, in which he would at first pretend to be a friend, acquaintance or admirer of the girls on social networking websites, such as MySpace and Facebook. Chansler used more than 60 different online screen names to conceal his identity and location, U.S. attorneys said.

After gaining some measure of trust from a particular minor victim, Chansler would request the victim engage in a live video chat session with him on the internet. During the video chat session, Chansler would use a computer program to record the video session without the knowledge of the victim, authorities said.

Chansler would ask the girl to expose her breasts or genitalia during the session. U.S. attorneys said Chansler would often entice the girls to expose themselves by showing them streaming video of a boy exposing himself or engaging in masturbation.

Unbeknownst to the minor victims, Chansler did not show himself during these webcam video sessions but rather would use sexually explicit videos of other boys he had collected, authorities said.

If a girl did expose herself to Chansler during a video chat session, this conduct would be recorded by Chansler. He then would send a copy or portion of the video recording to the girl. U.S. attorneys said Chansler would then demand the girl send him additional and more graphic sexually explicit digital still images or webcam video.

Chansler would inform the girl that if she did not comply with his demand, he would injure the girl's reputation by sending the sexually explicit images and/or videos to her friends, or by posting the images and/or videos to a public website, authorities said.

Some of the girls complied with Chansler's demands, while others did not. With some of those who complied, Chansler carried on a continuing pattern of extortion by sending more threatening communications and demanding additional sexually explicit images and videos from the minors, U.S. attorneys said.

On at least one occasion, Chansler was able to locate a girl who had established a new online persona in an effort to escape from Chansler. Authorities said Chansler had previously coerced the girl to produce and transmit to him dozens of sexually explicit images of her over an extended period of time. Using communications routed through a proxy server in Brazil, Chansler reestablished contact with this minor victim and continued his attempts to extort sexually explicit images from her, according to U.S. attorneys.

Using information received from the parents of one of Chansler's minor victims and working with the National Center for Missing and Exploited Children, FBI agents were able to identify Chansler and find his home in St. Johns County. On Jan. 8, 2010, law enforcement agents executed a federal search warrant at Chansler's home, authorities said.

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During the execution of the search warrant, Chansler was interviewed and told authorities he used social networking sites to meet girls who ranged in age from 13 to 18 years old. He targeted underage girls because adult women were "too smart" to fall for his scheme. The girls would agree to video chat with Chansler on a particular video chat website. Chansler said he saved all files he obtained from his victims in separate folders labeled with each victim's name, according to U.S. attorneys.

Subsequent forensic analysis of Chansler's computer revealed the computer contained two different hard disk drives, one of which contained images and videos of child pornography. The hard drive contained numerous folders characterized and labeled by the name of the minor victims. Authorities said many of the folders contained information specific to the particular victim, such as screen captures of the victim's social networking webpages, written logs of online chats between the victim and Chansler, and pornographic webcam videos and/or digital photos. In several of the videos, victims are seen crying and pleading with Chansler not to force them to engage in sexually explicit conduct.

The forensic analysis of Chansler's hard drive revealed he had targeted 350 different minor victims. Among these were 103 minor victims who have been positively identified. In total, Chansler's computer media contained 80,000 images and videos, many of which depicted what appeared to be post-pubescent minors engaged in sexually explicit conduct. Over 3,000 videos were recovered, and at least 200 of these videos depicted child pornography, authorities said.

U.S. attorneys said Chansler has been in the custody of the United States Marshals Service since Sept. 2, 2010.