The fact the impact points are spread out also indicate rockets rather than mortar.
The largest US mortar is the M120, a 120mm, with a range of 7.2km so drawing a circle from the center of the Green Zone will establish potential firing locations. Narrow the area of interest to known ISIS hot areas and start checking rooftops for evidence. Due to size/weight considerations of the baseplate, this is likely a smaller mortar so the actual range will be reduced along with the potential firing sites.
Abu Grab (sp) ISIS held.
The fact the impact points are spread out also indicate rockets rather than mortar.