Withholding or altering exculpatory evidence has long been considered an major violation of a prosecutor's duties. After all, "Society wins not only when the guilty are convicted, but when criminal trials are fair," as Justice William Douglas wrote in 1963's Brady v. Maryland. The consequences for violating that duty can include overturned convictions, mistrials, and damaged careers.
Soon, those consequences could include a felony conviction. Earlier this month, Governor Brown signed legislation that ups the penalties for prosecutors who alter or withhold evidence, making what was previously a misdemeanor a felony crime.