It was originally streamed on Hulu, which I do not subscribe to. https://en.wikipedia.org/wiki/The_Looming_Tower_(miniseries)

But my cable TV package here in Switzerland does provide BBC2, which began airing this series last night.

It's based on Lawrence Wright's book "The Looming Tower: Al Qaeda and the Route to 9/11." https://en.wikipedia.org/wiki/The_Looming_Tower

Jeff Daniels and Tahar Rahim, who play FBI Agents John O'Neill and Ali Soufan respectively, are both excellent so far.

If you haven't yet seen it and are able to do so somehow, I highly recommend that you do.