What happens if a person made a deal with prosecutor then it was discovered the person lied?

…The lie: I didn’t do anything much, person y was the one who did all the crime I was just there or something like that.
But video tapes found later show they did everything equally.

So they both committed a crime and then one was offered a deal to rat on the other? I’d think any story that one told would be verified thoroughly by the prosecutor. They wouldn’t just take the criminal’s word for it, they’d investigate it. In order to have any court case or deal, it’s got to consist of more than just the word of a criminal.

Yeah. The prosecutor runs the risk of being disbarred if they know their witness lied.

Prosecutors as a general rule cannot “promise less time in prison”. Sentencing is not up to them. What they can do in some cases is to make lesser charges: manslaughter, for example, instead of criminal murder, or negligent homicide instead of manslaughter. The sentencing guidelines differ for the crimes, but there can be overlap, too, and a judge who hears the case can, after the jury brings in a “guilty” verdict (and assuming that happens, if there is a trial) make a maximum sentence based upon what he hears.

Of course, if a plea deal is reached, then an allocution as to the facts and events of the crime is generally part of the deal: the guilty person has to say out loud – to confess – “what he did”, and perjury is still a chargeable offense separate from the crime that is being confessed.

Video tapes can’t always show conclusively that two criminals ‘did something equally’. Mens rea – “guilty mind” – is part of every actual crime: did the person know that what he was doing was a crime? Did he act freely and without coercion of some kind? Was he sober, sane and in control of his thoughts and actions? Videotape doesn’t show that, and most camera evidence is inconclusive even in the best cases.

Also in general when a prosecutor makes a deal for one criminal to turn state’s evidence on another, the deal goes to whoever makes the first admission of guilt, and implicates the other one. The prosecutor isn’t there to finely balance the scales of justice. He’s there to move meat through the system and make convictions without committing gross injustice (at least provable corruption) himself.

This whole scenario is the basis of the Prisoner’s Dilemma, which is a relevant part of Game Theory in these cases.

Plus it’s always assumed defendants are lying. They find that kind of thing all the time. Prosecuters don’t just take the client’s word blindly. They have to have proof.

Correcting myself: person x probably said they didn’t commit as many crimes (torture and murder of multiple victims/) not that they were just there.
@jca “They wouldn’t just take the criminal’s word for it, they’d investigate it” But they make mistakes too, they are human.

@CWOTUS Thanks for the correction yes, lesser charge promised by prosecutor, not less time in prison. But is the plea deal only valid if the story by person x is not contradicted by evidence at any time, in the future, right?

They don’t offer lesser charges unless they are certain that the other guy is the more important guy. The don’t just offer it because the dude says, “I didn’t do it!” If there is video evidence they will see that before offering any deal.

@flo: You can’t go to court or prosecute someone with just stories. You need evidence.

@jca There must be cases out there where prosecutors found out they made an error of making a deal with person x, after the case (after person x and y started serving their sentence). I guess they must be misinterpreting, or something, the “evidence”.

It’s up to a judge and a jury to decide upon their guilt or innocence based on the verdict, not the prosecutors.
If they find specific evidence and it was learned that the defense council team deliberately withheld it, that’s grounds for the defense council to be disbarred.

If they find evidence that says he didn’t do it, the judge can grant a new trial.