The criminal records system California is so poorly maintained that it routinely fails to alert officials to a subject's full criminal history.
The computerized log exists to provide an instant snapshot of a criminal past, informing police, regulators and potential employers of offenses such as murder, rape and drug dealing in a person's background.
But nearly half of the arrest records in the database don't say whether the person in question was convicted.
Information from millions of records buried at courts and law enforcement agencies has never been entered in the system.
"There are obviously serious public safety implications if that database is incomplete," said Dennis Henigan, president of the Brady Center to Prevent Gun Violence.
California has a shoddy system for collecting case results from 58 county courts and hundreds of local prosecutors and police agencies, said Travis LeBlanc, a special assistant attorney general who oversees technology operations in the state Department of Justice.
The final outcome "- guilty, not guilty, case dismissed" is missing for about 7.7 million of the 16.4 million arrest records entered into state computers over the last decade, according to LeBlanc. More than 3 million of those are felony arrests.