A homemade video showing a teenage girl tossing puppies into a fast-moving river provoked an international furor last month. Responding to strong public pressure and aided by some internet detectives, police in Bosnia tracked down the teenage perpetrator — but have reportedly let her go without facing charges. Here's an instant guide to this strange saga:

What exactly happens in the video? 
The 44-second video shows a girl clad in a red, hooded sweatshirt taking squealing puppies from a bucket and tossing them roughly into a river, where they almost certainly drown. If you haven't yet seen it, says Chris Matyszczyk at CNET, "you haven't missed much. Just arrant cruelty delivered with a youthful smile." (Watch the disturbing video here, with the proviso that it contains troubling footage of animal cruelty.) 

Why did it become so notorious?
The video provoked widespread public outrage after appearing on YouTube in early September — it has since been removed — and then being reposted on the 4chan internet forum and LiveLink. An internet-wide effort sprang up to find out who the girl was, with several Facebook groups dedicated to the purpose. Amid the general anger over her actions, some online commenters were were calling for her arrest and even death.

Have public figures weighed in on the video?
No less a "someone" than Michael Bay, Hollywood director of Bad Boys and Transformers. He offered a $50,000 reward to whoever tracked down the girl in the red sweatshirt. Twilight fans may also be interested to know that Kellan Lutz, the actor who plays Emmett Cullen in the tween trilogy, tweeted of his digust for the video. "It is plain out wrong," he said. 

Who is the puppy-throwing girl, then?
She is a teenager from Bugojno, a large town in Bosnia. The police have not named her, but she has reportedly posted an apology to YouTube in which she names herself as Katja Puschnik.

Has she explained her actions?
In the apology video, "Puschnik" says she killed the puppies because they were ill with parasites and she thought drowning them would be a "short death." "I did not want to make them suffer," she adds. "I am really sorry for this." The veracity of the apology video is unconfirmed. 

How did the police track her down? 
Animal protection groups in Bosnia received tips from amateur internet sleuths who had managed to identify and locate the owner of the YouTube account to which the video was posted. According to 4chan users, the video was filmed by the girl's brother, who then posted it online.

Why did the police let her go?
Police in Bugojna say they will not prosecute the teenager as she is too young to face court. The authorities added that the puppies were rescued from the fast-flowing river shortly after the video was shot — a claim dismissed by animal rights campaigners. "This is outrageous," a PETA spokeswoman said. "The puppies would never have survived in that river."

Is this an isolated incident?
It's just the latest in a series of viral videos of animal cruelty that has provoked a wave of outrage online. Most recently, footage of a middle-aged British lady throwing a cat into a garbage can led to death threats after she was identified — again, by users of 4chan — as Mary Bale of Coventry in the United Kingdom. That video has since become an internet meme, prompting parodies such as a video in which a man in a cat costume throws a middle-aged lady into a garbage can.

Why do these animal cruelty videos generate such an enormous response? 
It's notable that many atrocities committed against humans elicit relatively little popular response compared with stories about helpless animals, says author Shankar Vedantum. That's probably a function of how the human brain is wired: Large-scale tragedies often seem "abstract," while smaller-scale ones are felt "viscerally." Another reason for the fascination with this pair of videos is they both involved women, suggests author Herzog Friday in an interview with Salon. Apparently, between 90 percent and 95 percent of incidents of animal cruelty are carried out by men. "That's one reason why this went viral," says Friday. "It's the surprising idea of women being cruel in this way." 

Sources: Gawker, New York Daily News, CNet, New York Times, Salon

This article was originally published on September 7, 2010 and updated on October 6.