Double Jeopardy Technicality?

I'm not sure if someone convicted of a crime can later be tried for conspiring to commit that crime instead of having committed it, but then I'm not sure why anyone would do that. After all, in your scenario, the person has already been convicted of the crime. If he actually committed that crime, and it is later discovered that he had a partner with whom he conspired, then the authorities would simply try him for conspiracy in addition to the original conviction. There wouldn't be any reason for the prosecutor to choose between the two charges: someone can be guilty of both a crime and conspiracy to commit that crime.

On the other hand, if a person is convicted of a crime, and it is later discovered that he is actually innocent of that crime, but that he conspired with someone else to commit that crime, there might be some double jeopardy implications. It all depends on whether or not conspiracy is considered a "lesser included offense" to the actual crime. Criminal law isn't my specialty, so I don't know the answer to that question.

I think the answer to that is "it depends." If the elements that need to be proved to establish that the defendant committed the crime are also the elements that need to be proved to establish that the defendant was involved in the conspiracy, then conspiracy is a lesser included offense, and charging him with conspiracy after already trying him for the crime would amount to double jeopardy. That's the lesson of Rutledge v. US, 517 US 292 (1996) (which isn't, strictly speaking, a double jeopardy case, but it's close enough).

On the other hand, if the elements of the crime and the elements of the conspiracy are different, then conspiracy is a separate offense and there's no double jeopardy. So, for instance, in Rutledge, a defendant was charged with conspiracy to sell drugs and running a criminal enterprise to sell drugs. The elements of those two offenses were essentially the same (colluding with others to sell drugs), so the court held that he couldn't be convicted of both. In contrast, if a defendant is charged with murder and with conspiracy to commit murder, I would guess that the elements of the two crimes are sufficiently distinct that the defendant could be convicted of both crimes.

To me this seems like double jeopardy even though they are trying him for a different aspect of the same event, it is still referring to the exact same event. Does anyone know if there is an example of this ever occurring in case history?

The planning of a murder with another person, conspiracy, is not considered the same event as the murder. It is illegal to conspire with someone to commit a murder, regardless if the murder is actually committed.

I am saying the crime was actually committed. I want to know if it has actually be committed, the the criminal has already been convicted, can he then be tried for conspiracy and has it ever happened?