Police say a trucker from Mooresville harassed a teenage girl from Montana into sending naked pictures of herself via cell phone, then tried to blackmail her into sending him more sexual images.

Theodore Castine, 53, is being held by federal officials in Mecklenburg jail on charges of coercing a minor to engage in sexually explicit conduct across interstate lines.

The girl and her parents contacted federal agents in September, saying the girl had been contacted by a person on Facebook, asking, then daring, her to send "bikini" pictures of herself, according to an affidavit by a detective in Montana, where the family lives.

The man, who told the teenager he thought she was "hot," said he wanted her to pose in a sexual manner. To demonstrate what he wanted, he sent the girl two pictures of what appeared to be other teenage girls, exposing their private parts and posing in a lascivious manner, according to the affidavit.

The affidavit says the teenage victim tried to avoid sending the man naked pictures, but the man began harassing and threatening her.

"The subject made statements making the teen believe if she didn't send naked photographs, like those that had been sent to her instructing her how to pose, the subject indicated he/she was going to find the teen and she wouldn't like what was going to happen when the subject found her," according to the affidavit.

The teen said she felt compelled to send the man two naked photos of herself.

After that, the girl notified her parents, and later investigators, who searched the girl's phone and Facebook account.

At that point, a detective began communicating with the subject, posing as the girl.

The man, according to the affidavit, began to say the girl would have to send more photos, or the two she'd already sent would be posted on the Internet.

The man even gave instructions on how to take pictures with a friend's phone, remove the phone's memory card and send the photos by e-mail.

As investigators gathered more data about the man they believed was sending the threatening messages, he began getting more insistent.

"(Expletive), today. Get them done. Borrow a camera ... You better (expletive) send." The message also said: "Your friends will get them if you don't send more."

Another message simply said "Now."

On Oct. 18, agents went to Castine's home.

According to the affidavit, Castine said he owned the phone, knew the Montana girl was 14 years old, and admitted to exchanging pictures with her using the Internet. He also acknowledged befriending other underage girls.