In this series, Newsweek maps the road to 9/11 as it happened 25 years ago, day by day.

Yesterday: The news that Ahmad Shah Massoud had been killed “made me feel sick to my stomach,” said the CIA officer who led the first team into Afghanistan after 9/11.

September 10, 2001: Osama bin Laden telephoned his mother in Syria on September 10 to tell her that he might not be able to meet her for a while because “something big” was going to happen that would end their communications for a long time.

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Mohammed bin Laden and his wife, Alia Ghanem, a Syrian, gave birth to Osama (“young lion” in Arabic) in Riyadh on March 10, 1957. He was the seventeenth of 52 children sired by the elder bin Laden, who over the years took 11 different wives.

Bin Laden’s father ended up being Saudi Arabia’s wealthiest construction magnate and a close friend of the Saud royal family, granted many contracts to build basic infrastructure in the country and then to renovate Islamic holy shrines.

When he was three, Osama’s mother divorced Mohammed, and bin Laden was raised by his mother’s second husband in Saudi Arabia. He grew up and attended school mostly in Jeddah, joining the Muslim Brotherhood at a young age.

Armed masked men stand guard as suspected terrorist Osama bin Laden (C) and Ayman Al-Zawahiri (L) address a news conference May 26, 1998, in Afghanistan.

The young Osama went to Pakistan (and then Afghanistan) after the Soviet invasion in 1979 and there became connected with a number of soaring Islamic radical intellectuals. His main work during the Soviet occupation was caring for Afghan and Arab fighters and refugees and in monitoring Saudi and Gulf state young men who came to Afghanistan to wage “jihad.”

There was no contact between the CIA and bin Laden during this period, as he generally dealt with the governments of Pakistan and Saudi Arabia.

With the Soviet withdrawal in 1989, the CIA also withdrew all of the support for its covert action program against the Soviets and maintained no significant assets within the country. Little was known about bin Laden other than that he was one of many financiers of radical and terrorist groups.

In 1993, a special unit was established within the CIA Counterterrorist Center (CTC) called the Bin Laden Station that focused on developing intelligence on the financier.

Through 1998, when the two African embassies were attacked in August, the CIA worked alone and with friendly foreign intelligence services to disrupt bin Laden, degrade his ability to engage in terrorism, and bring him to justice.

The Joint Inquiry concluded after 9/11: “Between 1996 and September 2001, the counterterrorism strategy adopted by the U. S. Government did not succeed in eliminating Afghanistan as a sanctuary and training ground for Usama Bin Ladin’s [sic] terrorist network. A range of instruments was used to counter al-Qa’ida [sic], with law enforcement often emerging as a leading tool because other means were deemed not to be feasible or failed to produce results.

This image taken from a collection of videotapes obtained by CNN shows members of the upper echelon of the terrorist group al Qaeda: Ayman al-Zawahiri the second in command (L) and Osama Bin Laden the leader (R) after a press conference on May 26, 1998 in Afghanistan.

While generating numerous successful prosecutions, law enforcement efforts were not adequate by themselves to target or eliminate Bin Ladin’s sanctuary. The United States persisted in observing the rule of law and accepted norms of international behavior, but Bin Ladin and al-Qa’ida [sic] recognized no rules and thrived in the safe haven provided by Afghanistan….

“Despite intelligence information on the immediacy of the threat level in the spring and summer of 2001, the assumption prevailed in the U.S. Government that attacks of the magnitude of September 11 could not happen here.

“As a result, there was insufficient effort to alert the American public to the reality and gravity of the threat.”

Twenty-five years ago, on the morning of September 11, 2001, 19 al-Qaeda terrorists hijacked four passenger aircraft in a coordinated attack on the United States.

American Airlines Flight 11 and United Airlines Flight 175 were flown into the North and South Towers of the World Trade Center in New York City. Both towers later collapsed, killing office workers, emergency responders, airline passengers and people on the ground.

A third aircraft, American Airlines Flight 77, was crashed into the Pentagon in Arlington, Virginia. The fourth, United Airlines Flight 93, was heading towards Washington, D.C., but crashed in a field near Shanksville, Pennsylvania, after passengers and crew attempted to overpower the hijackers.

The attacks killed 2,977 victims, excluding the 19 hijackers, and injured thousands more. They were the deadliest terrorist attacks in American history.

The events prompted the United States to launch the “war on terror,” invade Afghanistan to target al-Qaeda and the Taliban government that sheltered it, and introduce major changes to aviation security, intelligence gathering and domestic counterterrorism.