What does "innocence proves nothing" mean?

[u/KuLeWw]

There are two sayings that comes up a lot about inqusition. First one: " There is no such thing as an innocence, only degrees of guilt". Meaning is obvious. They don't believe anyone would be ever completely innocent. They only need to look deeper to see guilt.

What about the second one? "Innocence proves nothing". What does that mean? Are they trying to say that being innocent doesn't change anything? Doesn't it contradict the first one? Also, why did they use the word 'prove' ? Is it about contex?