The IWI Tavor is the civilian version of the TAR-21 which was fielded by the Israeli Defense Forces in the early 2000s as an M16/M4 replacement. The TAR-21 would later be replaced by the more compact X95.
The Tavor is a bullpup configured rifle, putting the action of the rifle behind the trigger group. This configuration has some advantages, chiefly a shorter overall length. It also shifts the weight to the rear, which some operators feel makes it easier to handle when shouldered. Bullpup’s do have some shortcomings – reloading is akin to playing a violin, and requires some training. Also, the triggers rarely feel as good as other rifles do to the required extra linkage.
To my knowledge, this is the first case of a domestic terrorist using a Tavor or any bullpup rifle. Let me know in the comments if you are aware of any others.