Here in corruption-intensive Illinois, we’re being entertained by a trial of a guy who appears to be a major fixer, string-puller, influence peddler, etc. In various testimony given so far and apparently to come as a result of plea bargaining, our illustrious and wildly popular (at least within selected parts of his own family) governor’s name has come up. Can this testimony, which has been given under oath, become “truth” that can be used in a trial of this governor, should he be indicted at a later date for corrupt behavior? Do statements that are made in a trial become facts that can be used in other cases?
Yes, prior testimony can be used in later trials. In the case that I just finished they used prior testimony in their questioning several times in an attempt to use the persons earlier statements to impeach their current testimony.
They shouldn’t become “truths” just because someone said them in court under oath. People can and do commit perjury under oath. They do become a matter of public record that a defense attorney or prosecutor can referance when building a case.
I should have touched on that point. The statement doesn’t become truth, it simply becomes part of their testimony which can and should be evaluated by the jury in the case in question as to it’s level of truth.
However, under certain circumstances, it can be considered binding as against the party who made it.
That’s why I mentioned impeachment of testimony in my first reply. 
No.
A decision in the other case can be considered binding in certain cases (called either res judicata or equitable estoppel, depending upon the situation). Evidence, however, is always just that, evidence.
Now, if in the other case, there was an admission that was stipulated to by both parties as being true, that’s different.
Ok, but once the first trial is over, isn’t the testimony available to be used as evidence in future trials? And wouldn’t that testimony be the equivalent of a deposition? It’s a fact accepted into the record, isn’t it? Or is my grasp of law that distorted?
Yes, it can be used in future trials, but no, it’s not a fact.
Just because someone said it in court, even under oath, doesn’t make it so. Even if the jury/judge ruled in favor of the witnesses side, that still doesn’t make it a fact (they might have decided based on other evidence).
The only fact is that it was said in court. So that fact can then be used in another court, and the prior statements can be presented as evidence. But it’s still the jury’s job to decide if they believe that evidence. And that a previous jury might have believed it doesn’t mean this jury has to.
Maybe I’m mixed up on the issues here, but can an attorney reference X’s testimony if X is now dead? Or does it somehow run afoul of the right to confront one’s accuser?
THAT depends upon the situation. It is, for example, at issue in a case argued recently before the Supreme Court of the United States. The statement the prosecution wished to use was from the victim, who died at the hands of the defendant (the defense is that he acted in self-defense). The defendant wishes to keep the statement out of evidence, on the theory that he cannot cross-examine the person who made the statement. The prosecution argues the defendant should not be able to profit from having killed the person who made the statement.
Look for a decision by June. 
In most situations, testimony from another proceeding would be considered “hearsay.”
However, hearsay is potentially admissible if it’s a party’s statement being used against him or her.
Not always. For example, suppose a third-party witness W testifies about the facts of a traffic accident in a criminal prosecution of Driver X. In a later civil suit between Driver Y and Driver X, witness W would possibly have to be called back to testify. I don’t think you could rely just on the transcript of W’s testimony from the criminal proceeding.