A U.S. soldier is accused of shooting nine children, three women and four men in a house-to-house rampage in villages near his combat outpost in southern Afghanistan on Sunday.

The incident has sent ripples across the U.S. and the world, sparking threats of revenge from the Taliban, concern about the political implications of the attack and outrage from villagers.

There are more questions than answers around this horrific attack: What exactly happened when the soldier entered those villages Sunday? Who was the soldier behind this attack? Why did he do it? What are the political ramifications of this attack? And how will it affect the goal of peace in Afghanistan and future U.S. relations with the country?

How much do we know about what happened?

The shootings are believed to have begun between 2 and 3 a.m. Sunday in Panjwai district in Afghanistan's Kandahar province when the soldier went from house to house opening fire, according to officials and witnesses from the village.

"One guy came in and pulled a boy from his sleep, and he shot him in this doorway," one mother in the village told CNN. "Then they came back inside the room and put a gun in the mouth of one child and stomped on another child."

While investigators try to figure out exactly what happened, villagers say that the evidence that remains from the shooting paints a grisly picture. Shell casings were strewn across the streets. A dead toddler with a blood-stained face was lying sandwiched between two other dead men in the back of a pickup truck. In another truck, not far away, a blanket covered the charred bodies of two more victims.

A local minister told CNN that one family alone lost 11 members during the shooting spree.

"Look at this. The bodies - they all belong to one family," a villager cried.

While the bodies are mostly now covered or have been removed, the reminders of what happened literally still stain the village.

The floors and the walls of several homes in this area are splattered with the blood of those ambushed during the early morning attack.

The attack has shaken residents of the area in the western part of Kandahar, which is known to have a strong Taliban presence. Villagers there told CNN they are enraged. Residents say they moved back to the village because people on the nearby military base had said it was safe to return home, and that nobody would bother them.

Now, men openly weep in the street. Dreams of peace are now replaced with much of sorrow, and many people are crying and trying, through tears, to come to terms with what happened in Panjwai. 

Who is the soldier accused in the shooting?

Details about the soldier are beginning to emerge, but they are sparse. So far, it's known that he was a qualified infantry sniper, according to a senior U.S. Department of Defense official. 

The unidentified suspect served three tours of duty in Iraq before being deployed to Afghanistan, said Gen. John Allen, the U.S. and NATO commander in Afghanistan. A U.S. military official, who asked not to be named because he was talking about an ongoing investigation, said the suspect is an Army staff sergeant who arrived in Afghanistan in January.

During the suspect's last deployment, in 2010, he was riding in a vehicle that rolled over in an accident, according to a senior Defense Department official, who also spoke on condition of anonymity. The sergeant was diagnosed with a traumatic brain injury after the crash but was found fit for duty after treatment, the official said.

Traumatic brain injury has become one of the signature injuries of the wars in Iraq and Afghanistan.

He had been stationed at Joint Base Lewis-McChord, a sprawling military installation between Tacoma and Olympia, Washington. A handful of soldiers from the base have been involved in violent incidents in the past few years, including four soldiers convicted of killing Afghan civilians in 2010 as part of a "kill squad." Also in 2010, three other soldiers "suffered dangerous public mental breakdowns" after returning from Afghanistan, with two of them shot to death by police, according to the Stars and Stripes military newspaper.

The suspect's family has been moved to that base for their safety, an official said.

In Sunday's incident, after an Afghan soldier alerted the U.S. military at the outpost of the soldier's initial departure, the U.S. military put up an aircraft to search for him. Soon after, Afghan civilians came to the gate carrying wounded civilians, the first indication the military had of the shooting. When the soldier turned himself over to the search party, he immediately invoked his right not to speak. He has been moved to Kandahar and put in pretrial confinement, a congressional source told CNN.

The soldier could face the death penalty, said Defense Secretary Leon Panetta, who spoke to reporters as he flew to the Central Asian nation of Kyrgyzstan for high-level talks Tuesday.

What are the security concerns after the attacks?

There are fears that Sunday's killings could reignite the anger that led to deadly riots directed at international forces last month over the burning of Qurans by U.S. troops. That was one of a string of incidents involving American forces that have recently strained ties between the United States and Afghanistan.

The Taliban has already warned there will be reprisals, perhaps violent ones. Members of parliament in Kabul have decided to close down the parliament in protest of the killings. Hundreds of Afghans took to the streets Tuesday to protest the killings as the Taliban threatened to behead "Americans anywhere in the country."

There is a lot of anger brewing in the village and across the country. There's a lot of speculation that this plays into the hands of the divisive Taliban, which is trying to say, "Look, you can't really trust these coalition forces who claim to be here to help you," said CNN's Sara Sidner, who has spoken to villagers.

The U.S. government, NATO and Afghan officials are looking into this. But the real concern for Americans is that there are a lot of people asking for swift justice and wanting the person who perpetrated this crime to be tried in Afghanistan.

And that's why some U.S. commanders in Afghanistan are tightening security to protect against retaliation. Some of the precautions were put in place after the Quran burning incident, a senior defense official tells CNN.

The measures include adding a second U.S. soldier to watchtowers, where before there was one American and one Afghan on watch. American and Afghan forces live together on many of the smaller bases and outposts, and on some of these, the U.S. has instituted a 24-hour guard for barracks.

Joshua Foust is a fellow at the American Security Project, author of "Afghanistan Journal: Selections from Registan.net" and a former civilian cultural adviser for the U.S. Army. He said that while the shooting is horrific, it isn't surprising.

"Sunday's mass murder is not a new outrage for Afghanistan," Foust wrote in a column for CNN. "While the deliberate killing of civilians is (thankfully) rare, many Afghans do not distinguish between accidental and deliberate civilian death."

He added that the event is not game-changing and that many residents aren't surprised when the U.S. kills civilians.

What are the political ramifications? Does this change the U.S. mission in Afghanistan?

Most people agree that this incident will again strain ties between the Afghan government and the United States.

President Barack Obama on Tuesday called the killing of Afghan civilians, allegedly by a U.S. soldier, "outrageous" and "unacceptable," and said he is "heartbroken" over the incident.

"The United States takes this as seriously as if it was our own citizens and our own children who were murdered," Obama said in a statement to reporters at the White House. He said he directed the Pentagon to "spare no effort in conducting a full investigation" of what happened, and pledged that "we will follow the facts wherever they lead us."

But Afghan President Hamid Karzai has said this is unforgivable and an act of terror, in his words. He also expressed his condolences to the families of the Panjwai incident in Kandahar saying "the incident was cruel and an invasion that caused great pain for the people of Afghanistan."

The incident also calls into question the chances for stability as the U.S.-led military mission shifts security responsibility to Afghan forces in coming months. Combined with other recent events that sparked anger and distrust between the Afghan and U.S. governments, this shooting may make things even more difficult.

Analysts and U.S. officials said Monday they believe the transition under way - which seeks to end the American-led military mission in 2014 - will remain on track, though the process may be more difficult.

"There is still no better option, and the Afghans still aren't ready to handle their problems without us, and I think they know that," Michael O'Hanlon, a senior fellow at the nonpartisan Brookings Institution, said in an e-mail to CNN.

Senate Majority Leader Harry Reid, D-Nevada, reacted to Sunday's shooting by adding to calls for bringing U.S. troops home from Afghanistan as soon as possible, while Republican presidential hopeful Newt Gingrich said the entire Afghanistan mission needs to be reassessed.

The Obama administration insisted Monday that the civilian killings, while tragic and horrific, would not change the goals or timing of the U.S. strategy to defeat al Qaeda in Afghanistan and turn over security responsibility to Afghan forces.

"This is a challenging time, there's no question," White House press secretary Jay Carney told reporters Monday. "I do not believe that this incident will change the timetable of a strategy that was designed and is being implemented to allow for the withdrawal of U.S. forces."

So what now? Analysts say time to evaluate U.S. strategy in Afghanistan

Seth Jones, a senior political scientist at the nonpartisan Rand Corporation research organization, said the Sunday incident "certainly adds to tension between the U.S. and the Afghans, but I don't believe this is a tipping point."

Jones said news of the attack was sure to travel quickly throughout Afghanistan, spread by mullahs in mosques, word of mouth and radio.

The government will probably depict the incident as the latest of many atrocities by both sides, noting Taliban killings of civilians, while the Taliban will try to portray it as another example of U .S. aggression, Jones added.

Many analysts say the first step toward any progress is going to be taking a hard look at the policy in Afghanistan.

Foust says there is a larger problem with the U.S.-Afghan relations, saying "the U.S. is fighting one war while the insurgency is fighting a very different one."

"Put simply, the U.S. never put in place the strategic and political framework to make much headway in Afghanistan," he wrote. "Despite the renewed push for negotiations with the Taliban, there is no political strategy for the country. There is no end state for the war, either - right now, the plan is to draw down to about 20,000 troops or so - similar to troop levels in 2008 - and stay that way for the indefinite future. That's not a strategy, and it's not a plan."

Jeremi Suri, a Mack Brown Distinguished Chair for Leadership in Global Affairs at the University of Texas at Austin, wrote in a column for CNN that said the U.S. has a "self-defeating cycle in Afghanistan" and U.S. leaders have failed to set and pursue achievable objectives there. Until those are made, and carried out, Suri says, no real progress can be made and opportunities for increasing violence will remain.

"The American soldiers in Afghanistan are fighting a war against an elusive enemy amidst a population that is increasingly resistant to American demands for assistance," Suri wrote. "Afghan citizens know that the United States is planning to leave soon, and they sense that the Americans they meet care more about an "exit strategy" than the welfare of their society. Afghan intransigence furthers the frustration and resentment among American soldiers, fueling violent behavior directed at innocent civilians."

– CNN's Sara Sidner, Chris Lawrence and Pentagon Correspondent Barbara Starr contributed to this report.