Yes. The Fifth Amendment guarantees that "No person… shall be compelled in any criminal case to be a witness against" themselves. Courts have interpreted this to mean that not only may a defendant refuse to testify, but that witnesses may refuse to answer certain questions on the grounds that they may be implicated in criminal activity.
No. While a defendant has a right to not take the stand, a witness does not. Once ordered to testify, refusing to do so may result in the witness being held in contempt of court. While a witness cannot refuse to take the stand, it does not mean they have to volunteer whatever information is asked of them.
Witnesses in a criminal case have to major rights:
1) Right to Not Incriminate Themselves
This is commonly referred to as "pleading the fifth." What that means, essentially, is that a witness is invoking their Fifth Amendment right not to be a witness against themselves. Again, this right does not mean a witness can refuse to testify altogether.
2) Right to Not Be Harassed
While this right is not found in the Constitution, nearly every evidence code has some type of rule forbidding harassing a witness. This means a lawyer conducting a direct or cross-examination cannot repeatedly ask the same question, become hostile towards or threaten a witness. It is worth noting, however, that if a witness becomes hostile or uncooperative, a lawyer may be able to ask more forceful questions.
Another facet of this right to be free from harassment comes under rape shield statutes in an evidence code. These are typically invoked in sexual assault cases, where highly sensitive and private information may be brought out in an attempt to discredit a witness. These rules typically forbid lawyers from asking about:
- Sexual history with people other than the defendant
- Number of sexual partners
- Sexual preferences
- Right to Have a Lawyer Present
This right comes from the Sixth Amendment right to effective assistance of counsel. However, witnesses may not always be advised of this right, and may consider asking the judge for permission to consult with an attorney or to have one present before taking the stand. This is particularly important to keep in mind for witnesses that are afraid that testifying may implicate them in criminal activity.
If you have been or believe you will be called as a witness in a criminal trial, it is essential that you consult a criminal attorney to help you prepare your testimony and to learn how to protect your rights. Even if you are entirely innocent, it is very easy for innocent behavior to be construed as culpable or complicit in criminal activity. An attorney can help you understand when to "plead the fifth."