Im seriously sorry about that bro. Granted it wasnt a firearm, bt i know what its like to lose something really important to me. Got my laptop and sketchbooks stollen at a con one time... granted it was my fault for leaving it unattended for a few minutes, but yeah, it is a horrible feeling to leave something for a few moments then find out its gone...
^Dont worry about your dad, im sure he didnt take it
^And dont let them get to you. You left it unconcealed in a moderately safe place, and the guy you depended on locking your car didnt, so dont take the blame so hard.