This fact does not make distribution a crime.
For example, environment harmful production may be a crime, but it is not consumers or distributors who are criminals.
It should be totally legal to distribute those videos, especially if it helps identifying the kidnapper. I think the case you presented here is even easier as those videos will not damage reputation of someone murdered, it is even more obvious it is not a mistake of murder victim than in a case of rape.
By the way, isn't it already legal? Parts of such videos (video footage of murderers performing their crimes and other evidence archives) were even put on TV.
Well I have no good source for this, lots of people believe it is legal here for example: https://www.quora.com/Why-isnt-footage-of-9-11-illegal-to-di...
Edit: how can I have good source anyway if it appears to be legal? There is no law saying "you can distribute snuff video".
I disagree. Production would be pointless without a way to distribute it.