Dar al Arqam also served as the offices of two islamic "charities" which are listed as front organizations for terrorist groups. After Timimi's conviction the rest of the people associated with him abandoned the mosque.
Timimi was also an activist at George Mason University.
One of the charities/front groups located at Timimi’s mosque the Dar al Arqam was the Muslim World League. Not sure what the other one is though I know there is some connection between Timimi and Benevolence Intl.