Being forced to prove your innocence happens all the time.
Let me tell you a true story of my life. I was a foster parent for years. A biological mother accused me of child abuse for the express purpose of getting her child returned to her quicker. This happened during a time when a local foster parent was recently found guilty of killing a child with a claw hammer, so the Department of Human Services was on notice.
Wayne County, the county where the biological mother was based, asked Washtenaw County, where I live, to interview me for them. So they did. And at the end of their 30 day investigation, Wayne County showed to Washtenaw that they had done absolutely no work of their own and were upset that the Washtenaw County interview recommended unsubstantiating the charge. Wayne specifically asked Washtenaw to just substantiate it and have it done, after, again, doing no research of their own. They never talked to the doctor, they never got a second opinion (even though the investigating doctor said in his report that the mother pressured him to label the injury as child abuse), they never did...anything.
Now, substantiating, what does that mean? That means that for all intents and purposes I would be guilty of child abuse without ever facing a jury. I'd be unable to become a teacher (which I was going to school for at the time), the adoption that I was working on would be canceled (and was on hold during that time), and all the other stigma that come with it. If that happened, I could ask for a review by the head of the local DHS office, who could choose whether to uphold the substantiation or withdraw it. There was no time table for how long he had to decide on it, and I discovered that even the 30 day investigation took, in the end, nine months, during which time I was very cooperative and agreed to several demeaning measures in order to try to speed the process along. I was even, around the five month mark, willing to take a polygraph, which was taken around the seven month mark, and passed, and still the investigation went two more months.
So, in the absence of Wayne investigating, Washtenaw launched an investigation and found that there was no reason to suspect I was an abuser other than the original doctor statement, which states on it that there was pressure outside of the doctor's medical opinion. A second opinion (which Michigan law says is required...unless DHS doesn't do it...honest, it says that) was never sought. Washtenaw again pressed for unsubstantiation, and again Wayne, who had done nothing, denied it.
Wayne then launched their own investigation and couldn't even find the doctor who made the original report. Couldn't find. A doctor. Who has to be licensed. Couldn't find him. And still. Insisted on substantiation. A group that was so incompetent that they couldn't even find their only real credible witness still pressed for me to get blackballed.
Eventually, I was unsubstantiated due to the fact that Washtenaw County had ethical investigators who actually made every effort to find the truth of the case, but had I lived 20 miles further east, I would have been screwed. And never seen a jury. So I have a lot of sympathy for Troy Anthony Davis. But I still realize that innocent people will occasionally get screwed by the justice system.