There's a 43 year gap between those stats. You've got the beginnings of a hypothesis, but I think you need a lot more data if you want to support it at all.
What is the hypothesis; black people killed Detroit?
Or it could be that an 82% black population indicates $SOMETHING, rather than "black people killed Detroit". When Gary, IN started to fall apart with the steel mills closing, my theory was that the only people left were the ones too poor to get out. Could be the same with Detroit. Or not, I don't know. But the demographics remain, and a drive down Woodward Avenue will confirm the numbers.
What does it mean though? Your hypothesis should be something more than there sure are a lot of black people there and then let people's imaginations fill in what that means based on biases and broad generalizations. An observation is not a hypothesis.