Thousands of ballots that have already been cast in Mesa County, Colorado are being examined for evidence of fraud after election officials identified at least a dozen fraudulent ballots.

On Thursday, Colorado Secretary of State Jena Griswold announced in a press conference Thursday that a criminal voter fraud probe was being opened in the county. “It appears that as of now approximately a dozen voters in Mesa County had their ballots intercepted before they arrived to them and cast without their knowledge,” she said.

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The fraud was discovered when election workers were going through the signature verification process. Staffers compared signatures on the ballots with those on file and uncovered discrepancies. When voters were contacted about the rejected signatures, in a process known as “curing,” election staff discovered that some of the ballots had been fraudulently filled out, according to a report from Newsweek.

Election workers were alerted to the scheme when a voter told Mesa County officials that they had not yet received a ballot or voted. Another voter stated that they had received a notification through the statewide voter tracking system, BallotTrax, which claimed their ballot had been received even though they had not requested or cast one.

When the county clerk’s office investigated further, they identified several ballots that had been signed by the same person. The findings were turned over to Mesa County District Attorney Dan Rubinstein’s office, who opened a criminal investigation.

To date, officials have identified at least a dozen fraudulent ballots. The county is now working to examine all of the 30,000 mail-in ballots received to date for evidence of fraud, according to a report from Colorado Newsline citing the county clerk.

Griswold told reporters that the victims will be receiving new ballots. “Colorado’s elections are safe and secure, and this attempt at fraud was found and investigated quickly because of groundbreaking tools that we have here,” Griswold said in the news conference.

Colorado is one of a handful of states that mails ballots to all registered voters regardless of whether they requested one or not.

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