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.
"It's ingrained in this culture to be brutal to your enemy," says Colonel Johnson, from Baton Rouge, La. "They look at us and wonder why we worry about such things. At the soldier level, they just have a different concept. We tell them: 'There is no correlation between beating someone [hard], and getting good information.' "
Iraqis agree that the US view can vary widely from theirs. The immediate reaction of the Iraqi captain in charge of the four accused off-duty and out-of-uniform soldiers - from the unit that in recent months has taken control of the former insurgent stronghold of Haifa Street - was to inform his superiors that "I don't want these men in my company."
But others say there is room for violence. Last February, an Iraqi policeman detailed to this correspondent abuse by the police in the Haifa Street area. They said measures included handling that verged on torture to extract confessions.
"We do it a different way" from the Americans, says an Iraqi Army officer who asked not to be named. "Saddam taught people to understand power - they need to be shown who has power.
"Sometimes Americans are too nice - they capture bad guys, and they release them and people outside ask: 'Why did you release them?' " says the officer. "I don't like my forces to use power all the time. At some point, you must be clever and decide when to use power, or to talk. But when we show the people power, that we are strong, they like that very much."
Even Major Abdul-Hameed understands the dynamic, though in his 18 months as an intelligence officer, he has been through three training courses on treatment of detainees and lectured groups of Iraqi officers. Recruits are given a booklet with guidelines.
"Everywhere, there are good and bad people," says Abdul-Hameed. "On Haifa Street, we have lost a lot of martyrs, and [soldiers] have lost a friend. They know who did it, and when they arrest and bring in [a suspect], they beat him from Haifa Street to here, because they can't stand seeing the terrorist."
The officer says that more than 90 percent of detainees arrive "without abuse. Hopefully, in the future, we can eliminate these [abuse] cases."
Iraqis and US forces have begun by improving conditions for Abdul-Hameed's detainees and others at the many initial holding facilities that have, until now, often run with little oversight.
But high-level US attention - in the form of visits to this base by one general twice in recent days, and by top military lawyers - has already brought change.
"This is a work in progress," says Sgt. 1st Class Jeffrey Almand, leading a visitor and Iraqi officers to the separate detention structure. Ringed with layers of barbed wire, it faces a blank wall, with a sand-bagged guard bunker in between.
"They are making strides in the right direction," says Sergeant Almand, from Ragley, La.
The three plywood-floor cages now have grungy mattresses to sleep upon. Three portable toilets have replaced the overflowing latrine. Up to 50 suspects were crammed into this sweltering space at a time, though a US military tent has now been put up for overflow.
Detainees are supposed to be held for no more than 24 hours before being released or sent to a larger facility. But overworked interrogators - often without a clear sense of procedure or authority - created a bottleneck. One prisoner was here 23 days, another 77 days. Two Iraqi judges came last week to deal with 27 cases. They held initial hearings and emptied the holding cage.
"The situation is definitely improving, and we are now directed to intervene in cases where prisoner abuse takes place," says 1st Lt. Bill Barthen, from Superior, Wis.
"I don't care if a certain prisoner will get 25 years, or be sentenced to hanging, or if he will be released because there is no evidence - I treat them all the same," says Abdul-Hameed, noting that Iraq's brutal recent past is "very sensitive."
"In this new regime, the time of unfair, unjust [measures] has gone - we can get confessions out of detainees without beating them," says the Iraqi major. "The page of darkness has fallen down."