Imagine this scene: a trial is underway. An immigrant from Yemen is on trial for drug dealing. It's an open-and-shut case: the defendant sold drugs to an FBI agent in a sting operation. The defendant claims that he was framed, that he thought he was working for the FBI, and that he had been set up by an informant as a personal vendetta. 

The star prosecution witness is the FBI agent, who is on the stand. The agent is asked if he knew that the informant in the case was considered "unreliable" by the DEA. The agent states that, no, as far as he was concerned, the informant was perfectly reliable.

The judge raises his eyebrows. "That's not what you said in your testimony at an earlier hearing," the judge points out.

Lawyers start murmering to each other, and one of them asks for a break. The prosecution lawyers huddle with the FBI agent.

A few minutes later, the star witness returns to the stand. The question is repeated, and the FBI agent acknowledges that he had, in fact, been told by the DEA not to trust the informant. In fact, the matter had been discussed at some length with both the DEA agent and the informant.

Now the judge is visibly angry. "Not only did you rely on an informant who had been fired by the DEA for lying, but you may have perjured yourself as well," he tells the witness.

After a short pause, the FBI agent responds: "Before I answer any more questions, your Honor, I would like to invoke my fifth-ammendment right against self-incrimination, and consult with an attorney."

As the people in the courtroom try to make sense of this latest development, the prosecutor is handed a note. She reads it, then stands up and addresses the judge: "Your honor, I have been instructed that the U.S. Attorney's office no longer wishes to pursue this case. We would move to dismiss all charges against the defendant."

Something from Perry Mason?

Maybe, but this scene apparently actually happened a few months ago (dramatic embellishments aside). You can read about it here.