An effort is under way to promote the rule of law among Iraqi troops who deal with detainees.
The argument erupted at a Baghdad tea house between two men and four off-duty Iraqi soldiers. The civilians were detained.
But when they arrived at the Iraqi unit's holding pen - part of a US military base in the capital - one bore unmistakable signs of abuse.
Iraqi officers documented the abuse with photographs and released the men for lack of evidence. Two of the off-duty soldiers however, were thrown into a grim detention cage, to await a court-martial hearing from the top brass of the 1st Brigade 1st Iraqi Army Battalion.
"Write this in your notebook," Maj. Abdul Kader Abdul-Hameed, the top intelligence officer for the unit, says emphatically to this reporter. "The kicking and punching of detainees is prohibited. We have other methods of interrogation - often eyewitness [statements] are enough [to determine guilt]."
That decision is part of an increasingly strident joint US-Iraqi effort to limit Iraqi abuse of detainees that - amid the heat of a vicious insurgency - threatens to undermine the rule of law.
But a generation of extrajudicial abuse under Saddam Hussein means that many street-level members of the Iraqi forces still resort to violence.
"[Prisoner abuse] is not something we see every day, but [weekly] we see a prisoner come in, and someone has gone too far," says US Army Col. Ronnie Johnson, deputy commander of the 256th Brigade Combat Team, which fields advisory teams for Iraqi units.
In the past two weeks, US forces have stepped up their intervention in such cases, and sought to make rudimentary detention centers more humane. But US officers say their perspective is often at odds with that of some Iraqi counterparts, who take a tougher line.
US insistence on breeding adherence to the law and detainee rights is further complicated by prisoner mistreatment scandals by US guards at Abu Ghraib, Guantánamo Bay, and in Afghanistan.
The US military reportedly tallied more than 100 allegations of such abuse between September 2004 and February 2005. Since then, at least 28 more have been counted. The problem prompted Gen. George Casey, commander of US forces in Iraq, to issue a letter in April to US advisers to Iraqi troops. "It is very important that we never turn a blind eye to abuses, thinking that what Iraqis do with their own detainees is 'Iraqi business,' " General Casey wrote in an extract first published by The Washington Post.