Foundation of Ethics

Here is a hypothetical thought experiment you are to analyze:

You are a city prosecutor, and a terrible crime has been committed in your city. A 7-year old girl has been kidnapped, brutally raped, tortured, and strangled to death. The case has become something of a cause célèbre, and people are up in arms, outraged, clamoring that someone be caught and prosecuted. All investigations have turned up no leads. Your police chief advises that he has determined that unless something is done soon riots will occur, with extreme violence planned, and that several deaths are to be expected; many other reports confirm this. Yesterday a severely mentally retarded homeless man was picked up by the police, after a complaint by a restaurant that he was lurking about the premises, eating scraps out of the dumpster. There is absolutely no evidence against this man of the crime against the child. If you frame him, and plant or fabricate evidence that may result in conviction, you will be able to avoid the riots and probable deaths that might otherwise result.

Would this be moral or immoral? Why? (125 words)