They didn't?
There was a Pakistani on staff in the city of Houston who applaudeded the attacks in an email to someone else. The email came to light when he was being investigated over soliticting co-workers for prostitution.
And in the days following the attacks, Fat Bastard Moore and LaRouchians were calling for confirmation that it was REALLY white “Timothy McVeigh types” who hijacked the planes.
The Left and Islamic Supremacists in our midst held their tongues a few days, but they just sheltered their thoughts. They didn’t shut up, just waited until they believed they had a friendly ear.