Primtara incident

The Primtara incident was an incident on Primtara in Primtara outpost where at least two rebel troopers of the Rebel Alliance were killed. Further investigations by Alliance Intelligence of ballistics, spectrographic analysis, and chemical processes, as well as reports of an Imperial presence on Primtara and the unconfirmed information of new Imperial units named SCAR squadrons, along with witness accounts, provided strong evidence that it was Task Force 99 who was behind the attack.

Source

 * Star Wars: The Rebel Files – Deluxe Edition