Challenged by the police's assessments that arrests can't be carried out based on just inappropriate text messages from a particular phone number, a mother went undercover to nail the child predator who lurked on her child's Facebook account, with only a Target bra ad as a tool.

A woman from St. Petersburg, Florida, was aghast when she learned that her 11-year-old child had created an account at Facebook in May. Not only did her pre-teen purposely defied her orders that she's too young to have a Facebook account, she got all the more rattled because she saw that a bearded, grown adult man, 23-year-old Michael Bradley, was communicating with her child.

"I unlocked her phone, and I discovered a grown man on Facebook trying to befriend her," the woman said in an interview with St. Petersburg, Fla., station WTSP.com. "I got terrified."

The two, it seemed, have been communicating for already some time since the girl has given Mr Bradley her phone number. The mother called Mr Bradley and told him to stop communicating with her daughter. But as it goes, he didn't stop.

As if on cue, Mr Bradley's text messages began to get increasingly inappropriate and even graphic.

"He asked whether she was still a virgin, wanted sex for her birthday and she'd skip school to meet him," police said.

But then, such evidences are still not incriminating enough to warrant an arrest.

"Just because someone texts something inappropriate doesn't mean there's sufficient evidence for an arrest. First, we have to establish the suspect is the person sending that text. Just because it's a particular phone number doesn't suffice. You need more evidence," St. Petersburg police spokesman Michael Puetz told ABC news.

Challenged and running against time, the mother took the matter in her own hands by playing undercover and posing as her child.

The mother continued communicating with Mr Bradley. What's more, the alleged child predator believed it was the pre-teen he was really communicating with.

As expected, Mr Bradley who has become so unwittingly engrossed with his potential new victim, asked for the inevitable - a nude picture of the girl.

It was a request the mother had been patiently waiting for, and one that she's most willing to give in.

At that time, the mother happened to be looking at a Target store circular and then noticed a picture of a young woman wearing nothing but a bra.

"I scrolled through the Target paper. I saw a girl in her bra, so I just grabbed my cell phone, took a picture of it and sent it to him," the mother said.

Could the bra on the Target ad looked something like this?

Pleased that his willing victim finally relented, he asked for more graphic pictures.

But in a seeming tug-of-war scheme, the mother "titillated" her child's sexual predator and replied back she will send him more photos if he sends his first.

Mr Bradley, all too willingly, texted and sent an inappropriate picture. Bingo, the mom then called police, armed with her evidence.

"When she received the photos with the suspect's face, that changed the dynamic. Now we could identify the individual and make an arrest," Mr Puetz said.

The next thing Mr Bradley knew, the police were already pounding on his door.

He has been charged with 16 counts, including unlawful use of a two-way communications device and distributing obscene material to a minor.

"I just thank God that I got a hold of it when I did. I can only image how far things could have gone if I would not have got a hold of it," the mother told 10 News. She said she hoped her experience would also be a catalyst for other parents to monitor their children.