BAGHDAD, Iraq, March 25 — Mohannad al-Azawi had just finished sprinkling food in his bird cages at his pet shop in south Baghdad, when three carloads of gunmen pulled up.
In front of a crowd, he was grabbed by his shirt and driven off.
Mr. Azawi was among the few Sunni Arabs on the block, and, according to witnesses, when a Shiite friend tried to intervene, a gunman stuck a pistol to his head and said, "You want us to blow your brains out, too?"
Mr. Azawi's body was found the next morning at a sewage treatment plant. A slight man who raised nightingales, he had been hogtied, drilled with power tools and shot.
In the last month, hundreds of men have been kidnapped, tortured and executed in Baghdad. As Iraqi and American leaders struggle to avert a civil war, the bodies keep piling up. The city's homicide rate has tripled from 11 to 33 a day, military officials said. The period from March 7 to March 21 was typically brutal: at least 191 corpses, many mutilated, surfaced in garbage bins, drainage ditches, minibuses and pickup trucks.
There were the four Duleimi brothers, Khalid, Tarek, Taleb and Salaam, seized from their home in front of their wives. And Achmed Abdulsalam, last seen at a checkpoint in his freshly painted BMW and found dead under a bridge two days later. And Mushtak al-Nidawi, a law student nicknamed Titanic for his Leonardo DiCaprio good looks, whose body was returned to his family with his skull chopped in half.
What frightens Iraqis most about these gangland-style killings is the impunity. According to reports filed by family members and more than a dozen interviews, many men were taken in daylight, in public, with witnesses all around. Few cases, if any, have been investigated.
Part of the reason may be that most victims are Sunnis, and there is growing suspicion that they were killed by Shiite death squads backed by government forces in a cycle of sectarian revenge. This allegation has been circulating in Baghdad for months, and as more Sunnis turn up dead, more people are inclined to believe it.
"This is sectarian cleansing," said Mahmoud Othman, a Kurdish member of Parliament, who has maintained a degree of neutrality between Shiites and Sunnis.
Mr. Othman said there were atrocities on each side. "But what is different is when Shiites get killed by suicide bombs, everyone comes together to fight the Sunni terrorists," he said. "When Shiites kill Sunnis, there is no response, because much of this killing is done by militias connected to the government."
The imbalance of killing, and the suspicion the government may be involved, is deepening the Shiite-Sunni divide, just as American officials are urging Sunni and Shiite leaders to form an inclusive government, hoping that such a show of unity will prevent a full-scale civil war.
The pressure is increasing on Prime Minister Ibrahim al-Jaafari, a Shiite, but few expect him to crack down, partly because he needs the support of the Shiite militias to stay in power.
Haidar al-Ibadi, Mr. Jaafari's spokesman, acknowledged that "some of the police forces have been infiltrated." But he said "outsiders," rather than Iraqis, were to blame.
Now many Sunnis, who used to be the most anti-American community in Iraq, are asking for American help.
"If the Americans leave, we are finished," said Hassan al-Azawi, whose brother was taken from the pet shop.
He thought for a moment more.
"We may be finished already."
The human rights office of the Iraqi Islamic Party, a mostly Sunni group, has cataloged more than 540 cases of Sunni men and a few of Sunni women who were kidnapped and killed since Feb. 22, when a Shiite shrine in Samarra was destroyed, unleashing a wave of sectarian fury.
As the case of Mr. Azawi shows, some were easy targets.
Mr. Azawi was the youngest of five brothers. He was 27 and lived with his parents. He loved birds since he was a boy. Nightingales were his favorite. Then canaries, pigeons and doves.
During Saddam Hussein's reign, he was drafted into the army, but he deserted.
"He was crazy about birds," said a Shiite neighbor, Ibrahim Muhammad.
A few years ago, Mr. Azawi opened a small pet shop in Dawra, a rough-and-tumble, mostly Shiite neighborhood in southern Baghdad.
Friends said that Mr. Azawi was not interested in politics or religion. He never went to the Sunni mosque, though his brothers did. He did not pay attention to news or watch television. This characteristic might have cost him his life.
On Feb. 22, the Askariya Shrine in Samarra was attacked at 7 a.m. But Mr. Azawi did not know what had happened until 4 p.m., his friends said. He was in his own little world, tending his birds, when a Shiite shopkeeper broke the news and told him to close. He stayed in his house for three days after that. His friends said he was terrified.
The day of the shrine attack, Shiite mobs began rampaging through Baghdad, burning Sunni mosques and slaughtering Sunni residents. Some Sunnis struck back and killed Shiites. The mayhem claimed hundreds of lives and exposed tensions that until then had been bubbling just beneath the surface.
Two Shiite militias, the Badr Organization, which once trained in Iran, and the Mahdi Army, the foot soldiers of a young, firebrand Shiite cleric, Moktada al-Sadr, were blamed for much of the bloodshed. Mr. Sadr's men often wear all-black uniforms, and many of the relatives of kidnapped people said men in black uniforms had taken them. Many people also said the men in black arrived with the police.
Around 9 on the night of the shrine bombing, a mob of black-clad men surrounded the Duleimi brothers, family members said.
The brothers lived in New Baghdad, a working-class neighborhood that is mostly Shiite. They were all gardeners and religious men who prayed five times a day. They had relatives in Falluja, in the heart of Sunni territory.
Where a family hails from in Iraq often reveals whether it is Sunni or Shiite. Nowadays, because of the sectarian friction, people are increasingly aware of the slight regional differences in accent, dress and name. Some first names, like Omar for Sunnis, or Haidar for Shiites, are clear giveaways. Others, like Khalid, are not. Tribal names can also be a sign.
A cousin of the Duleimi brothers, who identified himself as Khalaf, said the four men were taken at gunpoint from the small house they shared. The next day, their bodies turned up in a drainage ditch near Sadr City, a stronghold of the Mahdi Army. All their fingers and toes had been sawed off.
That same day Mushtak al-Nidawi, 20, was kidnapped. According to an aunt, Aliah al-Bakr, he was chatting on his cellphone outside his home in Bayah when a squad of Mahdi militiamen marched up the street, shouting, "We're coming after you, Sunnis!"
Ms. Bakr said they snatched Mr. Nidawi while his mother stood at the door. His body surfaced on the streets seven days later, his skin a map of bruises, his handsome face burned by acid, his fingernails pulled out.
"I told his mother he was shot," Ms. Bakr said.
Sheik Kamal al-Araji, a spokesman for Mr. Sadr, said "the Mahdi Army does not commit such crimes."
He also said the militiamen would soon change their uniforms so they would no longer be confused with thugs.
The question of who exactly is behind these collective assassinations has become a delicate political issue. So has the disparity in the killings.
Many Sunni politicians, including secular ones like Methal al-Alusi, accuse the Shiite-led government of backing a campaign to wipe out Sunnis. Many Shiite leaders, including Prime Minister Jaafari, blame "foreign terrorists," without being more specific.
Zalmay Khalilzad, the American ambassador, has expressed increasing alarm about militia violence, saying it is a bigger killer than car bombs, the former No. 1 security threat. But he has been careful to paint the problem in broad strokes, implying both sides are at fault.
There are a few Shiite victims, such as Mohammed Jabbar Hussein, who lived in a mostly Sunni area west of Baghdad. He disappeared on Feb. 26 and was found four days later, shot in the head.
But the militias under the greatest suspicion, and the ones with the strongest ties to the government, are Shiite. Maj. Gen. Rick Lynch, a spokesman for the American military, said Shiite militias have played a role in the killings and "the government of Iraq has to take action against the militias."
Then there is the question of prosecution. While countless Sunni insurgents have been arrested and tried on murder charges, very few Shiite militiamen have been apprehended.
Thamir al-Janabi, who is in charge of the Interior Ministry's criminal investigation department, declined to comment. So did several other Interior Ministry officials.
A new round of revenge attacks began March 12, around 6 p.m., when a string of car bombs exploded in Sadr City, killing nearly 50 civilians. Most security officials, Shiite and Sunni, blamed Sunni terrorists for the attack.
An hour and a half later, half a dozen gunmen arrived at Mr. Azawi's pet shop.
Wisam Saad Nawaf was playing pool across the street. He said a man wearing a ski mask arrived with the gunmen, who were not wearing masks, and that when they grabbed Mr. Azawi, the masked man nodded.
"He must have been an informant from the neighborhood," Mr. Nawaf explained.
Mr. Azawi got into a car. The gunmen closed the doors. The next morning Mr. Azawi's body was found at the sewage plant. Autopsy photos showed how badly he was abused. His skin was covered with purple welts. His legs and face had drill holes in them. Both shoulders had been broken.
His brother Hassan carries the autopsy photos with him, along with a pistol.
"I cannot live without vengeance," he said.
Hassan said there were a few Shiites at his brother's funeral, which he took as a grim speck of hope.
One week later, on March 20, the body of Mr. Abdulsalam, another Sunni, was found under a bridge. Mr. Abdulsalam, 21, worked with his father in a real estate office. His family said he was last seen in his BMW, stopped at a Mahdi Army checkpoint.