Paris police hunting for alleged sexual harasser caught on tape punching a woman in the face

Paris -- Authorities in Paris are pouring over neighborhood surveillance video, interviewing witnesses and seeking the public's help in finding an alleged sexual harasser who was caught on camera punching a woman in the face after his apparent cat-calling prompted the woman to tell him to "shut up."

After the victim, Marie LaGuerre, posted surveillance footage of the incident to her Facebook page, the jarring video went viral in France and around the world, prompting French authorities to launch an investigation yesterday.

In the video, taken by a sidewalk cafe surveillance camera and provided to LaGuerre by the cafe owners, the alleged aggressor can be seen crossing paths with LaGuerre as the two pass each other going in opposite directions.

He appears to make a remark on the silent video, and she appears to respond. He then grabs an ashtray from a cafe table and hurls it at her, before following her as she turns to confront him, just off camera.

The man then hits her in the face so hard that her head is knocked sideways - back into the camera's view, as stunned cafe customers scramble to confront the man themselves.

The video is so alarming that it has prompted more women in Paris to come forward with their own stories of sexual-harassment-linked violence on city streets, Claire Ludwig, a member of the French feminist organization “Stop Street Harassment,” told ABC News.

"It raises awareness regarding street harassment,” Ludwig said. “The video demonstrates why women are sometimes not feeling safe when walking in the streets.”

“It’s good to see all the support Marie has received. It also allows her to legitimize her decision to publish the video,” Ludwig said.

Sexual harassment on the streets of France has become so ubiquitous that a new law is set to be adopted by the French parliament this week that would impose minimum fines of 90 Euros ($105 U.S. dollars) for harassment in public, such as catcalling and whistling.

"The first fines should be handed out this fall," France's gender equality minister Marlene Schiappa said on Monday.

Ludwig said the impending law is vital to holding harassers responsible for their actions.

“Street harassment was not defined in French law so it’s a good step forward," she said. "Having a legal framework regarding street harassment is very important."

LaGuerre told the French news channel France Info that she decided to post the video online because she had had enough of the kind of harassment she said French woman are victimized by every day.

"The Internet can have a huge impact," she told France Info, "even though I did not think it would take that magnitude. Myself, I did not realize the seriousness of the aggression. But I still decided to talk about it so as not to be silent, to denounce the kind of things that happen to all women.

"I was really lucky that there was a video," she said. "It highlights the fact that women do not feel safe on the streets. This is really a huge social problem."

According to Alexandre Langlois, member of the French police agency Fédération de la Police - known as CGT, investigators have various means to trace the individual.

“Investigators are interviewing witnesses who saw the incident,” he told ABC News in a phone interview. “They can help us determine which direction the aggressor went after he flew the scene.”

“There are also many surveillance cameras in the streets of Paris that could help us understand the individual’s path," he added.

Finally, investigators are encouraging any of the tens of thousands of Parisians who have seen the viral video -- and the aggressor's face -- to come forward with any information they may have.