The riots are part of the story, but absolutely not the start. Population was significant declining before the riots. A number of choices, including a long history of racial segregation in housing before the 60s combined with US housing policy (the GI Bill) to create strong incentives for people to build new houses outside of the city. That, combined with a lack of dense housing in the city, created cascading problems that are difficult to recover from.
A good source on this topic is Thomas Sugrue's "The Origins of the Urban Crisis".
http://en.wikipedia.org/wiki/1967_Detroit_riot
Things got bad. The insurrection act was invoked. The US military was sent in. Black-white relations have been awful since.
Detroit has faced white flight like no other city. From 1.5 million in 1950 to 75 thousand in 2010.
http://en.wikipedia.org/wiki/Demographic_history_of_Detroit