A video clip shows Iraqi security forces wearing black masks directly shooting a demonstrator at close range in a market in the central city of Diwaniya.
The video is believed to have been filmed during the Internet outage in most areas between October 2 and 6.
The demonstrations were launched in the capital Baghdad and cities in the south on the first of this month.
The video was broadcast on social networking sites after the return of Internet service yesterday evening.
Before the shooting, the video shows a boy screaming at regular forces, and during the scream, he was shot in the head at close range from what he wanted.
The screaming of the people around him was then heard denouncing the action, followed by heavy gunfire in an attempt to scare the crowds and prevent them from approaching the security forces.