MONTREAL — A Quebec mother posed as her 12-year-old stepdaughter for four weeks on Facebook to catch an alleged pedophile, QMI Agency has learned.

Her sleuthing led to the arrest of Martin Schanck, 24, of Coteau-du-Lac, Que., who is scheduled to appear in court Saturday for allegedly luring five children on the Internet.

The mother, who withheld her name to protect her daughter, said her girl received a Facebook message in March from someone posing as a 14-year-old named Sabrina Poirier.

The conversation quickly took a sexual turn, the mother said. Sabrina sent a photograph of an erect penis, claiming it was an ex-boyfriend's. That's when the 27-year-old mother took action.

"We immediately called the police," said the woman, who lives in southwestern Quebec near the Ontario border. "Reading the conversation from the beginning, I immediately realized that Sabrina Poirier was actually a guy."

Provincial police took the matter seriously, telling the mother to continue the conversation so investigators could gather evidence.

"My first conversation with him was very difficult and very emotional," she said. "It was so disgusting."

The Facebook conversations continued for four long and painful weeks.

"Every time we talked about another subject, he always returned to what interested him: the penis," she said, still disturbed by the experience. "The more the conversation progressed, the more perverse the questions got. I cried a lot."

The horror story ended in mid-May when police called to say they'd arrested and charged a suspect.

All five alleged victims are elementary or high school-aged girls in Salaberry-de-Valleyfield, Que., 60 km southwest of Montreal.

"I hope that our story deters anyone who wants to do the same thing to other girls," the mother said.

Martin Schanck faces a maximum of 10 years in prison if convicted.