Nine building workers have died in Iraq after being arrested on suspicion of insurgent activity and then left in a closed metal container.
Three men survived the ordeal, police sources said, despite being left for 14 hours in the burning Iraqi summer heat.
They had apparently been caught up in a firefight between US troops and Iraqi gunmen, and were detained after takng an injured colleague to hospital.
Police commandos face numerous claims that they abuse and torture detainees.
Meanwhile, gunmen have attacked an Iraqi army checkpoint north of Baghdad, killing at least nine soldiers.
Police sources told the BBC that at least 12 men had been arrested on Sunday after they had taken a colleague to hospital in Ameriya with gunshot wounds.
A local resident, thinking they were insurgents, called the police, who sent commandos to arrest the men.
At about midday, they were put into a metal container and by nightfall eight prisoners were dead and three were in a critical condition.
The survivors were taken to a central Baghdad hospital where staff said a ninth man died.
The Iraqi capital suffers scorching heat during the summer months, with temperatures often reaching 50 degrees.
A doctor told the BBC that one of the survivors had said he had been given repeated electric shocks by the commandos.
The survivors were kept under police guard as they were treated and were taken away without being allowed to speak to journalists.
Recent UK press reports have alleged police commandos systematically torture and abuse detainees. The security forces themselves are the target of much of Iraq's insurgency violence.