Most of the law regarding discovery in criminal cases focuses on what the prosecution must disclose to the defense. After all, the prosecution is the side with the most information and resources. But, at least in some sense, discovery is a two-way street: Defendants have to turn over certain information to the prosecution. This obligation is referred to as reciprocal discovery.
Defendants have argued that forcing them to turn over evidence to the prosecution in advance of trial violates their Fifth Amendment right to silence and the privilege against self-incrimination. But courts have upheld so-called reciprocal discovery laws. (It's worth noting that in many cases, specifically those that settle well before trial, the defense doesn't end up turning anything over to the prosecution.)
Each jurisdiction has its own reciprocal discovery rules. Here are partial examples of the kinds of information defendants routinely must disclose:
It used to be that defense attorneys could hide the ball, then spring evidence and witnesses on the prosecution at trial. The theory was that the government had all the power and the defense should be able to employ the scant advantages it had. But that changed in relatively recent years. If anything, legislatures are likely to enact more discovery requirements for the defense—and judges are likely to uphold them. Part of the rationale for more discovery is that it facilitates a quicker resolution of cases. The more the parties know, the better they can prepare for plea negotiations or trial.