I am curious how you can use statements made by a witness at a previous trial in a re-trial.

When cross-examining a witness at the re-trial, if they give an answer that is contradictory to what they said at the first trial, what can you do?

If you have a copy of transcript can you question them about what they said at the first trial?

If you have a copy of transcript can you submit it during closing statements to show they made contradictory statements? Is the transcript treated like case law so you can submit the transcript during closing statements even if you did not mention it during cross examination, or do you need mention it in cross examination in order to be able to submit it?

And what constitutes perjury versus simply showing their statements are inconsistent and therefore unreliable?

For it to be perjury there has to be the intention to lie and obstruct justice. No idea how you could prove something like that - it probably has to do with motive and whatnot. Maybe if the trial is about careless driving or something related to an accident, if the witness is currently suing the defendant. If the testimony has contradictory statements, they also have to be important to the trial to be perjury. So if, for example, a police officer in a speeding trial testified that your car is blue and then in the retrial testified that it is red. Even if he lied on purpose, the color of the car doesn't matter to the speeding charge so it wouldn't be perjury. However I would argue that in either case it shows that the witness does not have independent recollection of the event and therefore the testimony is not admissible.

When should you submit to the JP? I would assume as soon as possible as to "not waste the court's time".