The first indication for President Obama that Osama bin Laden had been killed came when a Navy SEAL sent back the coded message to Washington that said simply, "Geronimo-E KIA."
Geronimo was the code name for the operation that sent two teams of 12 SEALS zooming by Blackhawk helicopters to a walled compound in Abbotabad, Pakistan, on Sunday to kill or capture the most wanted man in the world. Anxious White House officials weren't positive that they would find bin Laden in the fortress-like complex, that he might leave while the SEALS were en route.
The first encouraging word came at the beginning of the raid when the SEALS recognized the man who had eluded a U.S. manhunt for a decade. They sent back the message, "Geronimo."
After a 40-minute search of the compound, punctuated by firefights, bin Laden was dead, and the cryptic "Geronimo-E KIA" code sent relief through the White House. E stood for enemy and KIA for killed in action.
Bin Laden was shot twice, once in the head and once in the chest, a senior administration official told ABC News.
The SEALS words, however, were not sufficient proof that the mastermind of the 9/11 terror attacks was finally dead. As the evidence piled up -- verbal ID, face recognition analysis and DNA matches -- the White House debate continued. Obama ended the discussion with a terse, "We got him."
White House senior officials were still sorting through the details today of the dramatic U.S. raid on bin Laden in Pakistan.
Counterterrorism chief John Brennan told reporters that while bin Laden had vowed to go down fighting, in his last moments alive the master terrorist hid behind a woman.
The woman who bin Laden tried to use as a human shield was killed in the U.S. raid, Brennan said. Whether she shielded him willingly is not known.
Brennan said the woman was one of bin Laden's wives, but defense officials said it wasn't clear whether the woman was a bin Laden wife.
The force that swooped down on the world's most wanted terrorist has been identified as SEAL Team Six of the "Naval Special Warfare Development Group."
Brennan, a senior advisor on homeland security, said they were trying to "accomplish the mission safely and securely" for those involved and were not going to give bin Laden a chance to fire back on U.S. forces.
"He was engaged, and he was killed in the process," Brennan said. "If we had the opportunity to take him alive we would have done that."
Brennan called this operation a "defining moment" in war against terrorist groups where they "decapitated the head of the snake."
The three to four hours Sunday night when operation was ongoing, Brennan described as "one of the most anxiety-filled times" and that "minutes passed like days."
Brennan acknowledged that there were some who didn't think the president should have pulled the trigger on the operation to go after bin Laden, who believed it was too risky, it was not guaranteed that bin Laden was there or had concerns that the mission would not succeed.
Administration officials are now trying to decide whether to release photos of bin Laden's corpse. Releasing the photos would prove that the terror leader is dead, but some officials fear the gruesome nature of the pictures could fan anti-American sentiment.
President Obama Praised Anonymous Heroes Who Killed Bin Laden
"We may not always know their names, we may not always know their stories, but they are always there on the front lines of freedom and we are truly blessed," Obama said in a White House ceremony to honor Medal of Honor winners.
"As commander-in-chief, I could not be prouder of our men and women in uniform," the president said. "That is true now in today's wars, and it has been true in all of our wars and it is why we are here today."
Obama briefly but proudly addressed the top secret raid that killed bin Laden. "I think we can all agree this is a good day for America," he said. "Today we are reminded that as a nation there is nothing we can't do."
He gave special recognition in his speech to Secretary of Defense Robert Gates, calling him "one of the finest secretaries of defense in our history."
When the gunfire stopped, the SEALS quickly moved to determine his identity. Two of the women at the compound identified him and the military flew bin Laden's body to Jalalabad, Afghanistanto have his DNA tested for positive identification. SEALS measured the corpse and determined it to be over 6- feet-4. They then transmitted photographs back to CIA headquarters and agency analysts conducted facial recognition analysis. Their report concluded it was a 90 to 95 percent match.
Bin Laden's DNA was matched with at least two of his relatives, including one of his sisters who died in Boston and whose brain was kept by the United States. The result came back as a 99.9 percent match.
Bin Laden's body was then flown to the aircraft carrier USS Carl Vinson, officials told ABC News and he was buried at sea. The burial was done in accordance with Islamic law, officials said, although there has since been despute over that. A Muslim seaman conducted the process and said the prayers, with bin Laden's body wrapped in the "appropriate way" with a white sheet.
Obama administration officials said it was important to handle the body in accordance with Islamic practices so not to inflame the Muslim world.
Celebrations erupted over night in the United States after the president's televised announcement that "justice has been done." But by this morning the triumphant mood was tinged with caution as security forces braced for possible revenge attacks.
The United States first received a tip in August that the mastermind of the 9/11 terror attacks was hiding in a million-dollar mansion with 12 to 15 foot walls.
The evidence that bin Laden was hiding there was largely circumstantial and he had not been seen, sources told ABC News, and officials did not know where he may be in the sprawling compound that is located about 1,000 feet away from the Pakistan Military Academy.
Tip on Bin Laden Came From Gitmo Detainees
In March, Obama authorized the development of a plan for the United States to bomb bin Laden's compound with two B2 stealth bombers dropping a few dozen 2,000-pound bombs, sources tell ABC News. But when the president heard the compound would be reduced to rubble, he changed his mind because it would mean there would be no evidence to present to the world that the head founder and leader of al Qaeda was indeed dead. Plus, all 22 people in the compound including women and children and likely many neighbors would also be killed.
So he instead authorized this risky operation, scheduled for a time of little moonlight, so U.S. helicopters could enter into Pakistan low to the ground and undetected.
The operation was authorized Friday morning and was originally planned for Saturday night, but on Friday, for weather reasons, it was pushed to Sunday.
Four helicopters swooped in to the compound and the Navy Seals fought a close quarters gunbattle. They ordered bin Laden to surrender, but the 54-year-old who had vowed he would not be caught alive, refused. He was then shot dead. His son, Khalid, was also killed in the raid.
Bin Laden's death was marked by jubilance, as crowds gathered at Ground Zero in New York and outside the White House chanting "USA, USA."
Congratulations poured in, with even former vice president Dick Cheney, a leading critic of the Obama administration, congratulating the president.
"Today, the message our forces have sent is clear -- if you attack the United States, we will find you and bring you to justice," Cheney said in a statement.
Bin Laden's death also prompted security alerts in the United States.
In New York City, Police Commissioner Raymond Kelly ordered the shift that was to go off duty at midnight be held over this morning to increase police presence in the subway system during this morning's rush hours. He also ordered that all members of the NYPD remain alert in the aftermath of the announcement of bin Laden has been killed.
Security was stepped up at the site of the 9/11 attack and in New York subways.
Washington police were also put on heightened alert and officials said there would be a show of force, especially near transit hubs, hotels and government buildings.
Philadelphia's Police Commissioner Charles Ramsey instructed dispatchers to ensure there are hourly checks on all mosques and synagogues in the city and police were put a heightened alert until further notice.
U.S. embassies have been put on high alert since the news was revealed, and the Department of Homeland Security and the FBI are reminding security forces around the country to be vigilant for suspicious activity amid concerns about possible retaliation.
U.S. officials are wary that the celebrations could trigger violent outbursts overseas. U.S. military officials in Afghanistan have been given a clear message to pass down to troops that they want a low-key reaction to the news, without any gloating, and they say this message comes "from the top" in Washington.
A top al Qaeda commentator on the internet was already vowing revenge. "Assad al-Jihad2" promised to "avenge the killing of the Sheik of Islam," according to the Associated Press, and warned that the war is far from over.
Though the critical tip about where bin Laden might be hiding came in August, the pursuit to find and kill him was nearly a decade in the making. The hunt began with a tip from detainees at the Guantanamo prison for terrorists who described an individual close to bin Laden who delivered messages to and from him.
U.S. intelligence officials were eventually able to track down the specific name in 2007 and for years, they sought out information about him. They finally spotted him in 2009 and it took a while to follow him, sources say. All signs signaled to bin Laden being in the compound, sources say, even though intelligence officials never saw him outside.
In April, the Navy Seals ran two practice runs at the replica compound they built in the United States to practice the raid.
The next target for the United States is likely to be the number two in al Qaeda's chain of command, Ayman al-Zawahiri. Zawahiri, an Egyptian doctor, helped found al Qaeda along with bin Laden. Sources say intelligence officials will also likely target Anwar al-Awlaki, a former imam thought to be behind such attacks against the U.S. as the failed Christmas Day terror plot in 2009.
"Though bin Laden is dead, al-Qaeda is not," CIA Director Leon E. Panetta said in a message to employees. "The terrorists almost certainly will attempt to avenge him, and we must -- and will -- remain vigilant and resolute."
ABC News' Mike Boettcher, Richard Esposito, Jason Ryan, Brian Ross and Pierre Thomas contributed to this report.