B.) These criminals almost never use a rifle of any kind let alone an "assault rifle". They are using cheap handguns that are frequently stolen. This is also verifiable using the FBI crime database.
B.)taking guns away from law abiding citizens will not decrease the incidence of murder in America and we have decades of scientific evidence that confirms this.
Roughly 40% of gun deaths are suicide. The majority of the rest are gang-bangers and drug related.