He will be charged with something else pretty quick, so he had better get out of the US ASAP.
It's not as good as an acquittal, but it could effectively end any prosecution. If the mistrial was induced by prosecutorial misconduct and double jeopardy applies, then it is hard to see what else they could charge him with under the Blockburger test. They've already charged him with first degree murder and firearms offenses.
Civil rights.
The catch all for prosecution.
Or just put him in a civil trial till he dies of old age.