Matt Bevan

He became obsessed with researching Islamic extremism, and quickly became an expert on the growing threat of terrorism on American soil.

As he continued rising through the ranks of the FBI's counterterrorism department, he was cognizant of the importance of balancing the need to keep people safe with the infringement on their personal privacy.

Ordered liberty.

A balance between government surveillance and individual freedom.

In the US, the government surveillance side of the seesaw is populated by lots of different intelligence agencies.

There's local police and the FBI keeping an eye on people domestically, and the CIA keeping tabs on potential threats abroad.

But in the 1990s, that system had a serious flaw.

Each of those agencies gathered their own data, but sharing data between them was complicated.

To understand how bad the data sharing was, think about information being like marbles in jars.

The FBI has a jar of marbles.

The CIA has one.

And the local police have one.

Each agency controls their own information, their own marbles.

Sharing marbles between them is incredibly complicated.

This whole system keeps things secure, but it means they basically can't work together.

And that problem was going to come into sharp focus for John O'Neill.

As he probed the World Trade Center attack of 1993, he became interested in one particular marble...

he believed the CIA had.

One that most counter-terrorism experts at the time weren't paying attention to.

In 1998, ABC America reporter Chris Isham, a personal friend of John O'Neill, trekked for 10 days across Pakistan to interview the leader of a little-known extremist group called al-Qaeda.