Long-time federal prosecutor turned white collar defense attorney Peter Zeidenberg urges the federal government to adopt a practice of open-file discovery in criminal cases. You should read the whole thing, but it's hard to beat this conclusion:
Experience and logic suggest that prosecutors have great difficulty shifting
from their natural role as advocate to the impartial role required to determine
what evidence will be helpful to the defense. Only by taking the discretion out
of prosecutor’s hands, and mandating full and open discovery in all but the
rarest cases, can there be confidence that what occurred in Stevens will not
reoccur down the road.