Civilian population? Southern Israel? I think not. A quick look at UNGA Resolution 181 - the partition plan against which Israel declared its 'independence' and the US quickly recognised as the State of Israel clearly show Be'er Sheba, Ashkelon, Ashdod and Sderot all lie in the Arab partition. These are the only 'borders' in force and internationally recognised. So, until Israel makes peace Hamas (and Fatah) have fired their home-made rockets, not into Southern Israel, but occupied Palestinian territory.
from the article: Palestinian activists urge Hamas to probe own Gaza war crimes