I have dilemma with false implication.

Say implication $A\to B$ is false, then this means that $A$ is true right? (based on truth table)

**So I am confused how in practice from false conclusion you can prove that any premise is true?**

Examples.

*If Jon is guilty, he had accomplice.*

Now imagine that this implication is false because someone who said it lied for example.

Then it means that Jon is guilty right?
**But clearly in practice you can't prove that Jon is guilty?**

So my question is more on implication and its relation to truths in the real world.

Or another example.

*If $X$ is an even number, then $X$ is prime.*

This is false implication right?
Which means that $X$ is even.
But it is nonsense because $X$ is ANY number.

Or feel free to come up with other examples, I hope I made clear what confuses me?