Statistical data of guns used in murders?

The problem with statistics is who wrote them and who set down the parameters on what stats to collect. If suicides are to be counted as murders, if justifiable homicides are to be counted as murder. you see where I am going with this I am sure. If the person collecting these states is pro or anti of the issue involved has he biased his process into representing his own agenda? Statistics cannot be trusted if you don't know the rules of collection. Both sides of any given issue, for that fact all sides of an issue skew the facts to favor their argument.