Definitely murder but what type of murder is what caused the delay in some ways. DAs go for the charge they know will stick. They will never be able to prove Murder 1 or Murder 2 in Minnesota and the cop would walk with even an average defense attorney.
They have to go for the charge most likely to convict but we all know this is never going to trial. The DA cannot risk a jury letting him walk and the whole city burning down.
As Captain pointed out, the wrong charge from the DA leads to an acquittal .
They are still looking to see what to do with the other 3 cops.