As a witness, it is my job to present facts as I know them. As I am a witness for the prosecution, my facts are more suited to them. They will be using me to help reinforce their argument.

How can it sway the decision?

As a witness, I reinforce what the prosecution is saying.This will help sway jurors to believe that the prosecution is correct.

Guidelines or Parameters?

I have to follow all regular court proceedings. Also, most important, I must not knowingly tell false information. This could send ME to jail!