BOISE - A federal court judge has ordered the state of Idaho to release or re-try a man convicted of murder in a shaken baby case more than two decades ago.

U.S. Magistrate Judge Ronald Bush ruled Wednesday that Ada County would have 120 days to either release Edward Stevens or give him a new trial, in part because prosecutors earlier failed to disclose some favorable evidence to Stevens' defense attorney.

The judge also found that investigators failed to maintain the proper chain of custody for some of the evidence. Chain of custody rules are intended to ensure that evidence for criminal cases isn't tampered with.

The judge said the prosecutor should have discovered and disclosed that some of the key evidence used to support the shaken-baby theory came from tissue samples that may have been damaged by the embalming process.

Stevens maintains the child was injured during an accidental fall.