Osama bin Laden Dead

Osama Bin Laden is dead Facebook Page goes viral.

Celebrations erupted in the United States over the news that Osama bin Laden, the most wanted man in the world, was killed by American forces in Pakistan. But the triumphant mood was tinged with caution as security forces braced for possible revenge attacks.

President Obama announced in a rare Sunday night televised statement to the nation that bin Laden, public enemy Number 1, was killed in a raid by Navy Seals in Abbotabad, a scenic military town just 100 miles away from the capital Islamabad.

"We will be true to the values that make us who we are," Obama said in a late night address Sunday. "And on nights like this one, we can say to those families who have lost loved ones to al Qaeda's terror: Justice has been done."

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 18 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.

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.

The president wanted proof, and he wanted to minimize collateral damage, sources say. 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, did not surrender. He was shot twice in the head, and his body was quickly taken away by U.S. forces for a DNA test to confirm his identity.

Bin Laden's DNA was matched with that of one of his sisters who died in Boston and whose brain was kept by the United States.

Sources tell ABC News he was buried at sea in accordance with Islamic law.

The news was marked by jubilance, as crowds gathered at Ground Zero in New York and outside the White House in droves, 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.

There were even some unusual praises from groups denounced by the United States, like the Muslim Brotherhood.

"With bin Laden's death, one of the reasons for which violence has been practiced in the world has been removed," Essam al-Erian, a member of the Muslim Brotherhood's governing body, told Reuters.

Bin Laden's death of also prompted security alerts in the U.S.

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 also 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.