Who's behind Iran violence? Website posts video in name-and-shame campaign.

The Internet is emerging as a way to undermine pro-government vigilantes who attack protesters as police stand by.

Mir Hossein Mousavi, the defeated opposition candidate who is contesting presidential election results, called for a day of mourning on Thursday for those killed during massive – and, lately, largely peaceful – street demonstrations.

As Iran's protesters have been finding out this week, among the most dangerous men prowling the streets of Tehran are armed intelligence agents and pro-government vigilantes wearing everyday clothes.

When clashes erupt between riot police and protesters, these provocateurs materialize from nowhere to take part in the fight – brandishing pistols, knives, and clubs – before disappearing again.

But during the six days of protests that have rocked Tehran and a number of other cities over the contested election victory of President Mahmoud Ahmadinejad, these violent actions have been caught on film and are being put online in a name-and-shame attempt to stop them.

"We are now identifying them, one by one, [and] this really scares them," says an Iranian source in Tehran familiar with the website http://lebasshakhsi.blogspot.com, which has posted photographs of individual agents and posts any information the public shares about them.

Since the 1979 Islamic Revolution, shadowy vigilantes called "pressure groups," which often have close links to conservative and pro-government elements in Iran, have been used to attack reformists or liberals, or put down any street protest with violence.

Mr. Mousavi this week accused the government and its irregular forces of "appalling murder" carried out by "disciples of fraud and lies."

Police often stand by if such elements are active. But the Internet, which has played a critical role for pro-Mousavi supporters to spread news of rallies or hot spots, may be one of the few ways to undermine the vigilantes.

"The pictures are coming from all over," says the source, who could not be named for security reasons. "People look at them, some recognize them as their neighbors or someone they have once known."

The website emerged from Facebook, and, so far, shows nine images of Iran's myriad shadowy forces at work. The top image is a closeup of the helmeted man with an AK-47 assault rifle, a member of the ideological basiji militia who fired from the roof upon demonstrators on Monday, killing at least three.

Other images show men beating protesters or engaging in thuggish behavior – all with their faces clearly visible. One man rides on the back of a motorbike, tucking a pistol into his belt. Another holds a pistol in his left held while he drives on the street.

Yet another photograph shows a classic chagoo-kesh, the Persian word for street thug that literally means "knife-puller." But this is not a young punk. The image shows a middle-aged man with a gray moustache and wearing untucked short-sleeve white shirt, holding a long kitchen knife in his hand.

Details were not long in coming about the knife-puller: name, mobile phone number, home address, position in the Revolutionary Guards.

"We have his cellphone and home address," says the source. "He has left town!"