Of course voter turnout was low; it was a mayoral election in April, like the city of St. Louis, where only 58,303 valid, countable votes were cast at the same time. This only 5 months after 132,487 votes were cast for President.
Sounds like people in Ferguson are disillusioned. I don't blame them.
The turnout among black voters in the St. Louis area dropped quite a lot even in Nov. 2016 compared to Nov. 2012. In State Representative District 76 -- which has the highest percent of black population in the whole state of Missouri: over 97% black -- the drop from Nov. 2012 to Nov. 2016 was almost 28%. That's a lot of disillusionment.