ARLINGTON – An Arlington man could face more than 40 sex-crime charges after he posed online as his teenage son and persuaded underage girls to e-mail him nude photographs, police said.

John Randolph Burk, 50, also paid two girls, ages 14 and 16, to pose in sexual positions at his home while he took pictures and fondled the younger girl, authorities said. Detectives said he paid the girls as much as $40 for each session.

He was arrested Dec. 8 after a monthlong investigation and has been charged with 16 crimes against four teens, including indecency with a child, sexual assault of a child, sexual performance by a child and possession of child pornography.

Burk could not be reached for comment.

Police have identified five other teens from five states who sent him photographs while they were underage, and police are investigating more than 20 other possibly illegal photos dating to 2002.

"This is a 50-year-old man who is taking advantage of the vulnerabilities of teenage girls," said Christy Gilfour, an Arlington police spokeswoman.

Police say Burk used his son's online identity to prey on teenage girls. His son, who was also a teen at the time, is now 20.

The four girls connected to the current charges range in age from 14 to 16. Burk was released this month on $125,000 bail.

Several neighbors contacted Tuesday said they didn't know him well and were unaware of the arrest.

Burk has a criminal history dating back more than 30 years. He was convicted of carrying a prohibited weapon in 1973, burglary of a habitation a year later and indecent exposure in 1994.

Police knew nothing of Burk's alleged activities until an anonymous call to Crime Stoppers in November informed police that teenage girls were visiting the 50-year-old. Detectives said they discovered that Burk hired the 16-year-old during the summer for housekeeping work but then offered to pay her to pose nude. The girl later invited a 14-year-old friend to join them.

Police said the girls came from low-income households and were tempted by what they saw as easy cash.

"They were not accustomed to getting that sort of money," Gilfour said.

Ann Ashmead, a clinical social worker with the Arlington Police Department, said this type of behavior is not limited to children in lower income levels. Instead of a few dollars, it might take an iPod or concert ticket to persuade a middle-class teen to participate in similar sexual activity.

"The high-income kids can be tempted just as easily," she said.

Ashmead said teens often think of this activity as something they do now but don't consider as their future.

"There is no way for them to know the far-ranging consequences of their actions," she said. "Those pictures can live on forever."

Although the girls willingly posed nude and sent photos to Burk, Gilfour said, the public shouldn't forget that these teens are victims.

"What's import to remember is that this suspect was tricking these girls," she said. "He was gaining their trust by convincing them that he was someone who was their age. He was very manipulating. He was very flattering."

Ashmead said that parents should talk to their children about this case, alert them to dangers on the Internet and monitor their online activity closely. She said children are more likely to be victimized if parents aren't communicating openly with their children and keeping tabs on their online whereabouts.

"What the bad guy is counting on is that we aren't talking to our children," Ashmead said.

Arlington police are asking parents who think their children had any contact with John Randolph Burk to call 817-795-1803. While online, he used the following e-mail addresses: sweetguy_76106@msn.com, stevenburk1@msn.com, steve16b@msn.com and rachybabes@msn.com. His chat room screen names were Jburk1 and Johnburk1.