Defendants are often ordered not to have contact with a victim, witness, or co-defendant in the case. That includes third-party contact, meaning it is a violation of his or her release conditions for the defendant to pass messages to those people through you or someone else. If you contact those people, it may look like the defendant asked you to even if he or she did not.
In addition, it is illegal to tamper with witnesses. If you speak to a victim, witness, or co-defendant it may appear that you are trying to influence them and you may get into trouble yourself.