it wasn't 500 civilians lol it was around 100 civilians and around 50 militants, around 8 palestinians executed by hamas.
as for whether the civilian casualties are "murder," if the air force actually has a policy of killing civilians on purpose they don't do a very good job of it, since they...
http://en.wikipedia.org/wiki/Palestinian_rocket_attacks_on_Israel
they've been firing rockets at civilian communities since 2001 though, so Israel has to respond.