[dragonwriter]

> If we assume comparative negligence

Criminal responsibility doesn't work that way.

Heck, IIRC, civil responsibility for negligence usually doesn't work that way, even in jurisdictions with a comparative negligence rule, except between the plaintiff and the set of all defendants.

> Then are you arguing that that the cop should get 20 years for responding to a shooter threat and killing someone that he thought was reaching for a firearm and the kid that perpetrated the prank gets 2 years?

No, the cop should get 100% of the punishment for a crime somewhere on the range between voluntary manslaughter and murder (of the depraved indifference sort, which is typically second degree.) And the SWATter should get 100% of the punishment for filing a false police report and a homicide crime which might be any of involuntary (misdemeanor) manslaughter (if the false report is a misdemeanor in the jurisdiction), depraved indifference murder, or felony murder (of the false report is a felony.)