In science we create theories which come form hypotheses. Theories need to be proved. Facts may support, oppose, prove or disprove a hypothesis, this is not at all black or white. Facts are black or white regardles of sience.

Black and white facts are the person murdered, crime commited and some other person guilty. The hypothesis is who this other person is.

The fact that the person murdered is not the most dangerous for the person suspected support the hypothesis that this has been done to discredit him. (but doesn't prove or disprove the hypothesis).

The fact that nobody has been prosecuted supports the hypothesis that the suspect is guilty.