After helping government forces break Islamic State's grip over a strategic town just south of Baghdad on Saturday, Shi'ite militias decided it was time for payback.
A Reuters witness saw the fighters in green camouflage uniforms scream and swear at members of the Islamist group as they kicked and struck them with rifle butts in Jurf al-Sakhar.
As the angry crowd of militiamen around the unarmed militants swelled, shots rang out. The three men lay soaked in blood in the dirt with gunshot wounds to the head.
"Those dogs are Chechens. They don't deserve to stay alive. We took confessions from them and we don't need them anymore," said one of the Shi'ite militiamen.
The victory could allow Iraqi forces to prevent the Sunni insurgents from edging closer to the capital, sever connections to their strongholds in western Anbar province and stop them infiltrating the mainly Shi'ite Muslim south.
Asked why the three men were executed, an army officer in Jurf al-Sakhar said: "We don't need them anymore. Why should we keep them alive?"
Responding to the same question, a senior member of a local Shi'ite militia said: "When we liberated Jurf al-Sakhar we found the skeletons of innocent people they killed and never buried. They should face the same fate."
Islamic State, made up of Arab and foreign fighters, swept through the north of Iraq in June and controls large parts of the west as well.
Its fighters hold swathes of territory in neighboring Syria and the group seeks to create an Islamic caliphate in the heart of the Middle East.
The group has threatened to march on Baghdad, home to special forces and thousands of Shi'ite militias expected to put up fierce resistance if the capital comes under threat.
Jurf al-Sakhar looked like a ghost town. Many residents had fled the fighting. Islamic State fighters had for months used skilled snipers and roadside bombs to prevent Iraqi security forces and Shi'ite militias from advancing.
During that period Islamic State used secret tunnels built by Saddam Hussein to evade United Nations weapons inspectors to move and store weapons and supplies.
Iraqi forces brought in helicopter gunships and used rockets to build up pressure on the militants, who finally fled on Saturday.
