It's not a leap, considering his group had already been tied to the 1993 WTC bombing by 1996[0].

This reminds me, I've always been curious that in the year leading up to the attacks, the Taliban was a frequent feature on ABC News. Mostly for their defacing ancient historical sites from what I fuzzily remember.

0: https://www.state.gov/1993-world-trade-center-bombing/

The WTC was attacked in ‘93 by people affiliated with Bin Laden and there were numerous attacks on US interests leading up to 2001. In 2000, the USS Cole was attacked, for example, with a string of embassy bombings throughout the 90s.

It's not a wild reach - OBL was behind the 1998 embassy bombings (Kenya, Tanzania) and the 2000 attack on the USS Cole, making him pretty much the "badguy de jour" by 2001.

I don't think we knew, but it wasn't hard to guess.

Osama bin Laden declared war on the United States in 1996. He, and Al-Qaeda, had been connected to multiple terrorist attacks throughout the late 90s. The people who had bombed the World Trade Center in 1993 were trained by Al-Qaeda.

Massoud, the Taliban's sworn enemy in the North of the country, had just been killed by suicide bombers on September 9th. BBC World News were reporting about his murder while the 9/11 attacks were happening. Earlier in the year, he spoke at the EU Parliament and warned the US against Osama Bin Laden.

What I'm trying to say is that there were breadcrumbs in the public arena to make an educated guess the moment the second tower was hit.

Al-Qaeda had already bombed US embassies and the USS Cole, and affiliates were responsible for the WTC bombing. It's the first group you'd look to blame.